Improving durability and mechanical properties of self-healing concrete through calcium carbonate precipitation using bactéria

ABSTRACT

This research examines the self-healing ability and durability of self-compacting concrete (SCC) enhanced by microbial calcium carbonate precipitation using Bacillus megaterium (BM). To stimulate bacterial activity, Fly Ash (FA) and Alccofine (AF) were used as partial replacements for Ordinary Portland Cement (OPC) at 5%, 10%, 15%, and 20% by weight. Twelve SCC mixes were prepared to assess the combined effects of BM and mineral admixtures on mechanical and durability properties. The AF10FA10 mix, containing 10% AF and 10% FA, showed the best performance with a 28-day compressive strength of 46 MPa, a 19% increase over the control (AF0FA0). Flexural and split tensile strengths improved by 18% and 17%, respectively. Bacterial precipitation of calcium carbonate sealed micro-cracks, reducing water absorption and porosity by 15% and 32%. Acid attack resistance confirmed higher compressive strength retention after 28 days in H₂SO₄. XRD, FTIR, and TGA analyses revealed calcite formation and greater calcium silicate hydrate (C–S–H) gel content, indicating a denser matrix. Although a full life cycle assessment was not performed, cement reduction suggests lower embodied carbon. This approach offers a sustainable route to stronger, more durable AF-based SCC.

Keywords:
Self-healing concrete; Bacillus megaterium; Fly Ash; Alccofine; Microbial calcite precipitation; Durability; Sustainable construction

1. INTRODUCTION

Concrete is a widely used construction material composed of cement, water, fine and coarse aggregates. It is essential to the development of modern infrastructure including roads, bridges, buildings, pipelines, dams, and nuclear containment facilities due to its high compressive strength, availability, and adaptability. However, despite these advantages, concrete exhibits a critical shortcoming it is inherently prone to cracking. Cracks form due to shrinkage, mechanical loading, temperature fluctuations, and environmental exposure, ultimately leading to structural degradation. These cracks compromise durability by allowing water, chlorides, and aggressive chemicals to infiltrate the structure, accelerating the corrosion of reinforcement, freeze–thaw damage, sulphate attack, and microbial deterioration. As a result, the long-term performance of concrete structures is adversely affected. According to reports, approximately 50–65% of concrete roadways and 35% of highway bridges require premature repair or replacement due to structural deficiencies and durability loss [¹]. Several factors contribute to these failures, including design flaws [²], substandard construction practices [³] and physical or chemical deterioration arising from overloading, abrasion, carbonation, or improper material selection [⁴]. Traditional maintenance methods, such as epoxy injections or surface sealing, require manual intervention and are not cost-effective or sustainable in the long run. Therefore, there is a need for innovative, autonomous repair technologies that extend the service life of concrete while minimizing environmental impact.

One such innovation is microbial-induced calcium carbonate precipitation (MICCP), a natural biochemical process in which certain bacteria precipitate calcium carbonate (CaCO₃) in response to environmental triggers. When embedded in concrete, these bacteria can autonomously heal cracks by producing calcite, which fills and seals the micro-cracks, effectively restoring structural integrity [⁵, ⁶]. MICCP is emerging as a promising self-healing strategy for concrete infrastructure. The process typically involves the incorporation of bacteria into the concrete matrix along with a nutrient source, such as calcium lactate. Upon exposure to moisture or oxygen through cracking, bacterial metabolic activity resumes, leading to the precipitation of CaCO₃ at the crack interface.

The foundation for MICCP applications was laid by Purnell et al. [⁷] who demonstrated bacterial soil treatment to reduce permeability and porosity. Since then, several studies have explored the use of different bacterial species for self-healing concrete. Ureolytic bacteria like Sporosarcina pasteurii initiate calcite formation through urea hydrolysis, while non-ureolytic strains such as Bacillus megaterium use calcium lactate as a carbon source, making them more environmentally friendly and less ammonium-intensive [⁸, ⁹, ¹⁰]. A local study employed a combination of Bacillus megaterium, fly ash and alccofine to heal surface cracks in concrete elements [¹¹]. Cracks of 1 mm width were sealed effectively, and microstructural analysis using FTIR and SEM confirmed calcite deposition within the crack zones [¹²]. These findings indicate the feasibility of combining microbial healing with supplementary cementitious materials (SCMs) for improved performance. The current study builds upon this by exploring broader SCM integration and performance metrics. In addition to performance improvements, bacterial self-healing concrete aligns with sustainable construction goals. The cement industry is responsible for approximately 7% of global CO₂ emissions, largely due to the energy-intensive clinker production process [¹³]. Of these emissions, around 95% originate from raw material calcination, with the remaining 5% attributed to transportation and other processes [¹⁴]. Reducing the environmental impact of concrete production is essential for mitigating climate change. One effective approach is the partial replacement of Ordinary Portland Cement (OPC) with SCMs like fly ash and alccofine. These materials not only improve concrete properties such as strength and durability but also reduce carbon emissions and energy consumption [¹⁵].

Beyond material and environmental advantages, the efficiency of the MICCP process itself depends on multiple interrelated factors. First, the selection of the bacterial strain significantly influences the rate and extent of CaCO₃ precipitation. Non-ureolytic strains like Bacillus megaterium are preferred for structural applications due to their low environmental risk [¹⁶]. Second, the bacterial concentration must be optimized to ensure effective healing without negatively affecting concrete’s porosity or water-cement ratio [¹⁷]. Third, nutrient availability is critical; calcium lactate is often used as a readily available and safe nutrient source to support bacterial metabolism. Fourth, the carriers used to encapsulate and protect bacteria play a pivotal role in maintaining bacterial viability during mixing and curing. Materials such as lightweight aggregates, silica gel, and hydrogels have been explored as protective carriers that can release bacteria upon crack formation [¹⁸].

Despite these advancements, research gaps remain. Most existing studies focus on either microbial healing or SCM integration independently. Limited investigations have evaluated the combined influence of Bacillus megaterium, dual SCM replacement, and their effect on the mechanical, durability, and microstructural characteristics of self-compacting concrete (SCC). Furthermore, many studies overlook the impact of MICCP under aggressive environments such as acid exposure, which is critical for practical durability assessment. In several studies, fly ash and alccofine were combined with Bacillus megaterium for crack healing; Therefore, the present study aims to systematically assess the performance of SCC incorporating varying levels of fly ash and alccofine along with Bacillus megaterium. The investigation includes compressive, split tensile, and flexural strength testing, alongside durability tests such as water absorption, porosity and acid attack resistance. Microstructural characterizations using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) are employed to validate calcite precipitation and matrix densification. This study seeks to advance the development of sustainable, high-performance self-healing concrete by integrating microbial biotechnology with eco-efficient material design.

2. MATERIALS AND METHODS

2.1. Cement

In the research study, Ordinary Portland Cement (OPC) with a grade of 53 was utilized. The assessment of the physical properties of this cement was conducted following the guidelines outlined in IS 12269:1987. The outcomes of the tests on the physical and chemical properties are presented in Table 1.

Table 1
Physical and chemical properties of cement.

PHYSICAL PROPERTIES	VALUES	CHEMICAL PROPERTIES	VALUES
Fine modulus	7.5	Aluminum oxide Iron ratio	1.2
Consistency	30%	Ratio of Saturation	0.89
Specific gravity	3.02	Intractable Residue	1.72%
Initial and Final setting time	60 and 300 mins	Magnesium	1.12%
		Alkaline	0.58%
		Anhydride Sulphur	2.2%

2.2. Fine and coarse aggregate

In this research, locally available river sand, reduced to a particle size of 150 micrometers after transversing through a 4.75 mm IS sieve, was utilized. The specific gravity of the river sand, verified to be 2.65 and falling within Zone III as per Indian Standard IS 383:2016, was considered. The fine aggregate’s properties were ascertained following the guidelines of IS 2386:1963 [¹⁹]. For the study, graded aggregates with a size of 20 mm were procured from nearby crushing plants. The specific gravity of the aggregate was found to be 2.75, and its additional properties were determined in accordance with IS 2386–1963.

2.3. Fly Ash and Alccofine

In this study, Class F Fly Ash was used as a supplementary cementitious material (SCM), partially replacing Ordinary Portland Cement (OPC) in selected concrete mixes. Class F Fly Ash is known for its low calcium content and pozzolanic properties, which enhance long-term strength and durability and its chemical composition is provided in Table 2. Fly Ash was incorporated at replacement levels of 5%, 10%, and 15% by weight of cement to evaluate its influence on the mechanical and durability properties of self-compacting concrete (SCC).

Table 2
Chemical composition of Fly Ash and Alccofine.

SI.NO	CHEMICAL COMPOSITION	FLY ASH (%)	ALCCOFINE (%)
1	SiO2	63	32.40
2	CaO	2	46.70
3	Al2O3	23	15.54
4	Fe2O3	1	1.7
5	MgO	1.23	5.24
6	SO3	0.35	0.34

Alccofine 1203 is a commercially available ultrafine mineral additive obtained from high-glass-content slag through a controlled granulation and grinding process. It was used in this study at dosage levels of 5%, 10%, and 15% as a partial cement replacement. Alccofine 1203 is characterized by its low calcium silicate content and high fineness, which contribute to improved particle packing, reduced water demand, and enhanced workability of SCC. Its use also supports sustainability by reducing clinker content and CO₂ emissions. The combined use of Fly Ash and Alccofine was intended to explore their synergistic effects on bacterial self-healing efficiency and concrete performance. The mix proportions are detailed in Table 3, and the associated admixture information is shown in Figure 1. The chemical compositions of Fly Ash and Alccofine are provided in Table 2.

Table 3
Mix propositions.

MIX ID	FA	CA	WATER	CEMENT	AF	FLY ASH	WORKABILITY
	(KG/M3)						(MM)
AF0FA0	615	990	360	800	0	–	78
AF5FA0	615	990	360	760	40	–	80
AF10FA0	615	990	360	720	80	–	90
AF15FA0	615	990	360	680	120	–	98
AF20FA0	615	990	360	640	160	–	105
AF0FA5	615	990	360	760	–	40	79
AF0FA10	615	990	360	720	–	80	86
AF0FA15	615	990	360	680	–	120	98
AF0FA20	615	990	360	640	–	160	102
AF5FA15	615	990	360	640	40	120	109
AF10FA10	615	990	360	640	80	80	112
AF15FA5	615	990	360	640	120	40	100

Figure 1
(a) Alccofine 1203 and (b) Fly Ash.

2.4. Bacteria

Gram-positive Bacillus megaterium, commonly known as grass bacillus or hay bacillus, is a soil-dwelling bacterium illustrated in Figure 2. The culture used in this study was procured from the National Collection of Industrial Microorganisms (NCIM), Pune. It was cultivated on solid agar medium composed of 13 grams of nutrient agar dissolved in 1000 ml of distilled water. For incorporation into the concrete mix, the bacterial colonies were scraped from the agar surface, suspended in water and then manually dispersed into the concrete mix water. The bacteria were introduced in a freely suspended form that is without any carrier or encapsulation method. No centrifugation or filtration was performed. To sustain bacterial viability in the alkaline environment of concrete, 0.5% yeast extract by weight of cement was added as a nutrient source, consistent with standardized microbial concrete protocols. This dosage was sufficient to maintain activity for up to 28 days, as supported by mineralogical evidence.

Figure 2
Bacillus megaterium-bacteria culture.

While no immobilization techniques such as silica gel, lightweight aggregates or hydrogels were applied, the survival of Bacillus megaterium was supported by its natural spore-forming capacity, enabling resistance to harsh pH and moisture-deficient conditions. Routine sub-culturing every four weeks ensured culture purity and activity for experimental use.

Bacillus Megaterium is often employed in the development of self-healing concrete [²⁰]. This bacterium has the ability to produce calcite precipitation through metabolic processes, contributing to the sealing of cracks in concrete over time. This microbial-induced calcite precipitation (MICP) is a key mechanism in the self-healing properties of certain concrete formulations, where Bacillus Megaterium plays a crucial role in enhancing the material’s durability as shown in Figure 3. Concrete mixes with bacterial concentrations ranging from 1 × 10⁶ to 3 × 10⁶ cells/mL were tested. The optimal performance was observed at 3 × 10⁶ cells/mL equivalent to 30 × 10⁵, which yielded maximum tensile and flexural strength. This dosage enhanced calcite precipitation, contributing to improved crack healing and densification.Scaling up the bacterial concrete approach requires considerations such as bacterial storage, nutrient dosing and compatibility with industrial mixing and transportation. Ensuring bacterial viability during transit and curing is a practical challenge. Moreover, the cost of microbial cultures and their incorporation into batching protocols must be optimized to make this method viable for large-scale applications. Pilot studies at plant level are essential to validate industrial feasibility.

Figure 3
Bacterial cell concentration.

2.5. Concrete mix design

The concrete mix design in this study was formulated in accordance with IS 10262:2019 for M40 grade concrete, aiming for a target compressive strength of 35 MPa at 28 days, as shown in Table 4 [²¹]. The adopted water-to-cement (w/c) ratio was 0.4, and the mix proportion was finalized as 1:0.77:1.24 (Cement: Fine Aggregate: Coarse Aggregate). To enhance performance and facilitate microbial-induced calcium carbonate precipitation (MICCP), the concrete was modified with 0.5% Bacillus megaterium and 0.5% calcium lactate, both calculated by weight of cement. Calcium lactate, used in powdered form, was dry blended with the cement prior to mixing. A poly-carboxylate ether (PCE) based superplasticizer dosed at 0.8% by weight of cement, was incorporated to ensure proper flow characteristics and workability suitable for self-compacting concrete (SCC). In addition to the bacterial additives, the mix incorporated Alccofine 1203 and Class F Fly Ash as partial cement replacements at 5%, 10%, 15%, and 20% levels to study their synergistic effects on self-healing efficiency and durability performance.

Table 4
Mass, volume and density of SHC.

MIX ID	MASS OF ­CONCRETE SPECIMENS (KG)	VOLUME OF CONCRETE SPECIMEN (M3)	DENSITY OF CONCRETE (KG/M3)	POROSITY AT 28 DAYS (%)	REDUCTION IN POROSITY ­COMPARED TO ­NORMAL CONCRETE (AT 28 DAYS) (%)
AF0FA0	7.50	0.003375	2222.22	3.4	–
AF5FA0	7.30	0.003375	2162.96	3.1	8.82
AF10FA0	7.40	0.003375	2192.59	2.9	14.71
AF15FA0	7.15	0.003375	2118.52	2.7	20.59
AF20FA0	6.90	0.003375	2044.44	2.6	23.53
AF0FA5	7.15	0.003375	2118.52	2.8	17.65
AF0FA10	6.95	0.003375	2059.26	2.7	20.59
AF0FA15	7.40	0.003375	2192.59	2.5	26.49
AF0FA20	6.85	0.003375	2029.63	2.4	29.41
AF5FA15	7.30	0.003375	2162.96	2.6	23.53
AF10FA10	7.20	0.003375	2133.33	2.3	32.35
AF15FA5	7.58	0.003375	2245.93	2.5	26.47

To improve bacterial viability and distribution, Fly Ash was soaked in a prepared bacterial solution for duration of one hour prior to mixing. This pre-treatment step aimed to enhance bacterial attachment and activation. The bacterial solution was prepared using a predefined concentration and dissolved in water, which was fully included in the total water calculation to maintain the target w/c ratio. After soaking, the treated Fly Ash was added along with the remaining dry ingredients and aggregates for mixing. No chemical admixtures were used, as the workability was controlled only through water to cement ratio and SCM mixes. A total of 12 concrete mix combinations were developed and each included both bacteria and calcium lactate, as listed in Table 3. Specimens were cast and cured under standard laboratory conditions submerged in water for 28 days, following the IS 516:1959 procedure. While this standard curing method ensures consistency, future research will address curing under ambient or field-based conditions to evaluate the in-situ self-healing behaviour and long-term performance.

2.6. Carbon footprint

The environmental impact of concrete can be approximated by correlating its compressive strength and cement content to embodied CO₂ emissions, as supported by literature [²²]. An empirical model proposed byGowleski et al. [²³] offers a simplified method to estimate CO₂ emissions per cubic meter of concrete based on compressive strength in Equation (1):

(1) $${\text{kg of CO}}_{\text{2}}\text{per cubic meter of concrete =}\delta \sqrt{ClassofConcrete}$$

where δ is a coefficient with a default value of 46.5 MPa, empirically calibrated for standard OPC concrete. This value reflects typical cement consumption and production conditions in European practice. The appropriateness of δ for M40 grade concrete is assumed but should ideally be regionally recalibrated. Additionally, another simplified empirical relation in Equation (2):

(2) $${\text{CO}}_{\text{2}}{\text{(kg/m}}^{\text{3}}\text{) = 12}{\text{.5 × f}}_{\text{c}}$$

where, fc is the compressive strength (MPa). This formula assumes average cement content (around 350–400 kg/m³), standard energy mix, and OPC-based binder without SCMs. Based on Equation (2), the estimated embodied carbon for the control mix (AF0FA0, 39 MPa) is approximately 487.5 kg CO₂/m³, while for the AF10FA10 mix (46 MPa), the value rises to 575 kg CO₂/m³. However, these estimates do not reflect SCM usage. Since 20% of OPC is replaced by Fly Ash and Alccofine in AF10FA10, the net embodied carbon is reduced by ~15–20%, accounting for SCMs’ lower emissions.

This results in a likely adjusted value of ~475–490 kg CO₂/m³ for the AF10FA10 mix comparable or even lower than the control mix despite higher strength. These findings demonstrate that SCM-enhanced microbial concrete can achieve carbon efficiency without compromising strength. However, this model is limited by its assumptions: average OPC composition, standard curing, and no transport or lifecycle data. For more accurate environmental profiling, a detailed Life Cycle Assessment (LCA) using regional data, binder chemistry, and energy sources is recommended, as outlined in [²⁴].

2.7. Workability of concrete

Workability defines the ease with which concrete can be mixed, placed and compacted without segregation. In this study, workability was measured using the slump cone test following IS 1199:1959. The slump values, recorded in millimeters reflect the flow characteristics of each mix and are presented in Table 3.

3. RESULTS AND DISCUSSION

3.1. Mechanical properties of self-healing concrete - compressive strength properties

The assessment of materials, components, or structures often involves the measurement of compressive strength in Figure 4. Among the various tests conducted on concrete, the compressive strength test stands out as one of the most widely utilized, offering comprehensive insights into material properties. Each compressive strength value represents the average of three specimens and results are expressed as mean ± standard deviation (sd). The coefficient of variation (cv%) for each mix was within 3–6%, indicating good repeatability and reliability of the data are shown in Figure 5. This test is typically performed on hardened concrete cubes. The compressive strength test serves as a pivotal factor in evaluating this strength. While occasional tests on cylinders may provide insights into concrete strength, the standard representation of concrete strength is derived from testing cubes of specified dimensions. Standardized 150 × 150 × 150 mm cubes are commonly employed for this purpose, and in certain instances, 100 mm cubes may be used as an alternative or backup measure [²⁵].

Figure 4
Different mixes in casting and curing of cubes and testing.

Figure 5
Compressive strength of concrete.

Relative to the control specimen, concrete samples containing varying concentrations of bacteria exhibited enhanced compressive strength, with increases ranging from 25.40 to 26.34 MPa at 7 days, 33 to 34.6 MPa at 14 days, 39 to 46 MPa at 28 days, in Figure 6. The findings suggest that the concentration of bacteria, reaching up to 10⁶ cells/mL, positively impacted compressive strength compared to the control specimen. However, when the bacterial concentration increased to 30 × 10⁵ cells/mL, a reduction in compressive strength was observed compared to the 30 × 10⁵ cells/mL concentration. Furthermore, in contrast to control specimens loaded with 18% of compressive strength, the results revealed a significant improvement in concrete specimens when subjected to a 18% compressive strength load at 14 and 28 days, particularly showing improvements in the ranges of 25% to 30% and 35% to 40%, respectively. Biochemistry has contributed to the enhancement of compressive strength in concrete specimens by leveraging the effectiveness of microorganisms in depositing calcium carbonate within micro-cracks and voids [²⁶]. This process facilitates the healing of cracks under loading conditions, thereby improving the overall structural integrity of the concrete.

Figure 6
Flexural strength of concrete.

3.2. Mechanical properties of self-healing concrete - flexural strength of concrete

Flexural strength measures a beam or slab’s resistance to bending and is tested using a universal testing machine (UTM). In this method, unreinforced concrete beams of 100 × 100 × 500 mm dimensions, with a span length three times their depth (i.e., 300 mm) are loaded until failure occurs. The test procedure was conducted as per IS 516:1964, and the modulus of rupture (expressed in MPa) was recorded. Flexural strength typically corresponds to 15% to 20% of the compressive strength and is sensitive to mix proportions and curing conditions. The specimens were cured for 28 days and tested using a UTM with properly aligned loading surfaces to ensure accuracy. At 28 days, the control mix AF0FA0 achieved a flexural strength of 4.0 MPa, whereas the AF10FA10 mix reached 4.8 MPa, representing an 18% improvement. Failure load was measured at the point of cracking, and the corresponding flexural strength values are shown in Figure 6.

Concrete samples containing different concentrations of Bacillus megaterium demonstrated consistent improvement across all curing ages. At 7 days, flexural strength increased from 2.8 (control) to 3.2 MPa, at 14 days from 3.5 to 4 MPa, and at 28 days from 4 to 4.8 MPa. These improvements correlate with increasing bacterial concentration up to 30 × 10⁵ cells/mL, attributed to enhanced calcium carbonate precipitation which contributed to micro crack healing and matrix densification. The results clearly show that bacteria-incorporated SCC, especially mixes like AF10FA10, AF0FA15, and AF10FA0, demonstrate significantly higher flexural performance compared to the control. Figure 6 effectively illustrates these trends.

3.3. Mechanical properties of self-healing concrete - split tensile strength of self-healing concrete

The Split tensile strength of concrete was evaluated using a compression testing machine on cylindrical specimens following the IS 516:1964 guidelines. Each cylinder was positioned horizontally on the loading platform of the Universal Testing Machine. Load was applied along the diameter until the specimen failed in tension, providing a measure of concrete’s tensile resistance a valuable complement to flexural and compressive strength tests. As shown in Figure 7, concrete mixes containing bacterial concentrations demonstrated improved split tensile strength at all curing intervals. At 7 days, strength increased from 3.0 (control) to 3.7 Mpa at 14 days, from 3.1 to 3.8 MPa and at 28 days, from 3.15 to 3.8 MPa. The AF10FA10 and AF0FA15 mixes showed the highest strength (3.8 MPa), representing a 19% increase over the control. These improvements are attributed to microbially induced calcium carbonate precipitation (MICCP), which filled pores and improved the internal matrix.

Figure 7
Split tensile strength of self-healing concrete.

To support this mechanism XRD analysis confirmed the presence of crystalline calcium carbonate, validating the pore-filling hypothesis. The test results confirm that bacterial inclusion significantly enhances tensile properties in self-healing concrete. Among all, AF10FA10 exhibited the best performance, indicating optimal synergy between Bacillus megaterium and dual SCM replacement (Fly Ash and Alccofine).

3.4. Durability of self-healing concrete - water absorption of concrete

Figure 8 present the impact of adding various concentrations of bacteria to concrete specimens on their water absorption capabilities. The results indicate that, across concrete specimens aged from 10 to 15%, there was a consistent decrease in water absorption as the bacterial concentration increased. Specifically, when compared to the control specimen, the concentration of 30 × 10⁵ cells/mL demonstrated the most significant reduction in water absorption, showing a decrease of 15% in Figure 8. Additionally, Figure 8 which depicts the water absorption characteristics, uses the following Equation (3):

Figure 8
Water absorption of concrete.

(3) $$\text{Water}\text{Absorption}\text{(\%)}=\frac{Ws-Wi}{Wi}\times 1\text{0}0$$

Where Wₛ is the saturated surface dry weight and W_i is oven dry weight. This calculation method follows procedures similar to IS 1199 and confirms the improved permeability of bacterial concrete. The diminished water absorption observed in the concrete specimens can be attributed to the bacteria’s ability to deposit calcium carbonate layers within cavities, pores, and micro-cracks. This deposition effectively seals the pores and micro-cracks, leading to an improved permeability of the concrete material [²², ²⁷, ²⁸]. Upon examination of the concrete samples subjected to a load equivalent to 10% of their compressive strength, it became evident that there was a noticeable decrease in water absorption compared to the control specimen, registering a range of (15–18%). This reduction in water absorption can be attributed to the presence of bacteria actively contributing to the production of calcium carbonate (CaCO₃), subsequently reducing the pore percentage in the concrete material. The incorporation of bacteria seems to play a vital role in altering the water absorption characteristics of the concrete, emphasizing the potential benefits of microbial involvement in concrete properties.

3.5. Durability of self-healing concrete - porosity of SHC

The porosity of self-healing concrete refers to the measure of open spaces or voids within the material. In the context of self-healing concrete, porosity is a crucial property as it directly influences the concrete’s durability, permeability, and susceptibility to environmental factors [²⁹]. The self-healing mechanism in concrete involves the ability of certain materials, often bacteria, to promote the deposition of calcium carbonate or other mineral precipitates within cracks, pores, and voids in Table 4. This process can lead to the reduction of porosity in the concrete, improving its overall performance. As the bacteria contribute to the healing of micro-cracks, they effectively seal these voids, leading to a more compact and less porous concrete structure. Reducing porosity in self-healing concrete is desirable because lower porosity generally correlates with enhanced durability, increased resistance to freeze-thaw cycles, and improved resistance to chemical ingress. However, the specific impact on porosity can depend on the type of healing agent or mechanism used in the self-healing concrete, as well as the curing conditions and overall mix design.

A clear correlation was observed between lower porosity and increased compressive strength among the tested mixes. For example, the AF10FA10 mix exhibited a porosity of 2.3% and achieved the highest ­compressive strength of 46 MPa at 28 days. Similarly, AF0FA15 with a porosity of 2.5% also demonstrated improved tensile and flexural strength. This trend suggests that reduced pore connectivity and water absorption, facilitated by microbial-induced calcium carbonate precipitation contributed to enhanced matrix densification and strength development. These findings reinforce the interdependence between durability and mechanical performance in bacterial self-healing concrete. One limitation of this study is the absence of freeze–thaw durability testing. Since concrete in temperate regions is often subjected to cyclic freezing and thawing, future work should evaluate how bacterial calcite precipitation influences crack healing and durability under such dynamic environmental conditions.

3.6. Durability of self-healing concrete - acid attack test

In a 28-day experiment after casting, concrete cube samples from each mix were removed from the curing tank and air-dried for 24 hours. Their initial weights were recorded before beginning the acid exposure. The acid attack test followed by IS 516:1959 with modifications to accommodate sulphuric acid immersion, simulating long-term durability in aggressive environments. In this study, specimens were first cured for 28 days in water [³⁰, ³¹, ³²]. Then, for the next 28 days, they were immersed in a 2% sulphuric acid (H₂SO₄) solution with an approximate pH of 1.5, refreshed weekly to maintain acidity. The test evaluated acid resistance of the concrete mix by comparing compressive strength before and after immersion. Each test was conducted on three specimens per mix, and results represent mean values.Figure 9shows compressive strength loss in each case. Mixes containing bacteria and SCMs (AF10FA10 and AF0FA15) exhibited better durability, showing strength reductions of 18% and 20%, respectively. In contrast, the control mix (AF0FA0) showed a 45% strength reduction, and AF0FA20 showed 40%.

Figure 9
Compressive strength before and after immersion.

These findings indicate that self-healing concrete incorporating Bacillus megaterium and SCMs like Fly Ash and Alccofine can significantly resist acid-induced deterioration. This enhanced resistance is attributed to the calcite precipitation filling internal pores and reducing acid penetration, supported by XRD patterns confirming crystalline calcium carbonate formation. Figure 10, illustrates the visual appearance of concrete after 4 weeks of sulphuric acid exposure. The surface degradation in the bacterial mixes was visibly less compared to the control. Unlike traditional repair method such as epoxy injection which requires manual labour and has limited ecological value, bacterial self-healing concrete offers autonomous in-matrix crack repair improving durability with minimal post-construction intervention. For practical deployment, future work should include lifecycle cost-benefit analyses and field durability trials to validate long-term performance.

Figure 10
Visual appearance of concrete after exposure to sulphuric acid during 4 weeks.

3.7. Characterization techniques - XRD analysis

The X-ray diffraction (XRD) findings for fly ash and alccofine are shown in Figure 11(a). Quartz (SiO₂), which is present in a significant amount, is the main constituent influencing the mechanical qualities. Al₂O₃ is the second most common element after quartz and helps to improve mechanical characteristics and reduce porosity [³³, ³⁴]. The XRD data show peaks with high intensity, small breadth, and considerable quantities, which suggest the material’s crystallinity. When forming aggregates, these characteristic peaks which indicate a high degree of crystallinity are very helpful [³⁵, ³⁶]. According to the XRD investigation, the Fly Ash’s crystalline structure and content include components that enhance mechanical qualities and decrease porosity. Because of this, fly ash is a useful ingredient in the creation of concrete, demonstrating its potential to improve the material’s overall performance and durability. The analysis of concrete and bacterial mixes in Figure 11(a), XRD shows calcium lactate properties. Notably, the low intensity and broad bases of the peaks suggest that calcium lactate is an amorphous solid. Its amorphous form is characterized by the absence of a clear crystalline structure. The XRD data shows that calcium lactate has a significant proportion of calcite and quartz (CaCO₃) despite its amorphous makeup. Even in an amorphous substance, the existence of these distinct constituents indicates that they are essential parts of the composition. Despite being amorphous, calcium lactate’s components are clearly distinguishable. Calcite is especially significant because it helps precipitate calcium carbonate, which gives the material some of its cementitious properties. Quartz, on the other hand, is thought to increase the material’s strength. This information on the makeup and properties of calcium lactate is helpful in figuring out how it could affect the concrete mixture’s qualities. While this study examined strength and durability up to 28 days, long-term bacterial viability beyond this period remains to be evaluated. Although FTIR, TGA, and XRD confirmed calcite presence, Scanning Electron Microscopy (SEM) would offer direct evidence of crack filling and mineral deposition, and will be included in future investigations.

Figure 11
(a) XRD analysis of concrete and bacteria mixtures - (C-Calcite; F-Florite; H-Hematite); (b) FTIR analysis of concrete and bacteria mixtures; (c) TGA analysis of concrete.

3.8. Characterization techniques - FTIR analysis

The FTIR spectroscopy of several concrete mixes with mineral admixtures as the sole cement replacements is shown in Figure 11(b) after 28 and 90 days of curing, respectively. After 28 and 90 days of curing, respectively [³⁷, ³⁸]. After two and three months of curing, these figures show the results for concrete mixes that include varying amounts of both admixtures. The production of hydraulic compounds such as C–S–H is indicated by the discovery of unsymmetrical bending bonds in silicon oxide at an approximate distance of 1000 cm⁻¹. This finding emphasizes how important Si–O bonds are to the formation of important cementitious compounds in concrete mixtures. Three basic zones may be seen in the resulting infrared spectrum. Stretching vibrations are the defining feature of the first zone, which spans wavelengths between 850 and 1200 cm⁻¹. This range is essential for interpreting the material’s vibrational properties, which provide important information on the chemical makeup and bonding of the concrete mixtures. Identification of important chemical characteristics and compounds, such as Si–O bonds linked to C–S–H production, is made possible via FTIR spectra analysis [³⁹, ⁴⁰, ⁴¹]. This makes it easier to evaluate the concrete mixes’ performance in a more nuanced way by providing a thorough grasp of their composition and characteristics at various curing times. When particles are present, the FTIR data clearly show changes in the peaks when compared to the control mix. The hydration of C₃S and C₂S, two essential components in cementitious materials, is responsible for the discernible decreases in the intensity of the Raman bands at 1636 and 3400–3650 cm⁻¹ during the course of the curing time. Bands seen at 1417 and 750 cm⁻¹ also move toward the lower wavenumber side, more precisely between 1450 and 1460 cm⁻¹, when the fly ash concentration rises. The degree of carbonation correlates to these changes, revealing that the presence of nanoparticles helps to lower carbonation. Additionally, the bands at 960 and 980 cm⁻¹, which correspond to the minerals mono sulfate and C–S–H particles, respectively, migrate to the lower wavenumber side when the concentration of particles increases. This discovery suggests that the presence and concentration of admixtures particles affect the composition and properties of these cementitious compounds. Essentially, the FTIR data provide important information on the chemical reactions and changes that occur in the concrete mixtures, emphasizing the role that fly ash and alccofine play in the carbonation, hydration, and cementitious compound formation processes.

3.9. Characterization techniques - TGA analysis

Thermo-Gravimetric Analysis (TGA) is a technique used to study the thermal stability and composition of materials by measuring the weight change as a function of temperature or time [⁴², ⁴³, ⁴⁴]. In the context of concrete, Thermogravimetric analysis (TGA) can yield significant insights into the breakdown and thermal characteristics of the components shown in Figure 11(c). TGA is typically performed using specialized equipment known as a thermos-gravimetric analyzer. The equipment consists of a sample pan and a balance that continuously measures the weight of the sample as it undergoes thermal treatment [⁴⁵]. By combining TGA with other techniques like Differential Scanning Calorimetry (DSC) or Fourier Tranform Infrared Spectroscopy (FTIR), it’s possible to identify specific phases and reactions occurring during heating. TGA analysis in concrete can be used for quality control purposes in construction materials. Researchers may employ TGA to investigate the effects of different admixtures, curing conditions, or the impact of additional cementitious ingredients on the thermal properties of concrete. Analyzing the TGA data involves identifying peaks and patterns in the weight loss curve and correlating them with known reactions or components in the concrete mix.

The findings from the thermogravimetric analysis unveiled distinct temperature ranges associated with mass loss and the decomposition of individual components. Specifically, within the temperature range of 25 to 100 degrees Celsius, a significant weight loss was primarily attributed to the evaporation of pore water lingering in capillary pores [⁴⁶, ⁴⁷]. During this phase, weight loss was influenced by a combination of capillary pores, adsorbed water, and interlayer water. Subsequently, between 100 and 450 degrees Celsius, the second notable effect was observed as ettringite and C–A–H, two types of calcium silicate hydrates, underwent dehydration. At around 475–750 degrees Celsius, the third phase was typified by the disintegration of calcium hydroxide. The reaction between alccofine and calcium hydroxide, which results in the development of extra CSH (calcium silicate hydrate) gel, is the cause of the lower proportion of calcium hydroxide in alccofine concrete as compared to conventional concrete. In normal concrete, there is no constituent that engages in such a reaction with calcium hydroxide, resulting in a higher percentage of this compound in comparison to alccofine concrete.

4. CONCLUSIONS

This study investigated the mechanical performance, durability enhancement, microstructural changes, and environmental implications of self-healing concrete (SHC) incorporating Bacillus megaterium and supplementary cementitious materials (SCMs) such as Fly Ash and Alccofine. A total of 12 mix combinations were tested to identify the optimal self-healing formulation. Among all tested mixes, AF10FA10 consistently outperformed others across all strength metrics. At 28 days, it achieved the highest compressive strength of 46 MPa (a 19% increase over the control), flexural strength of 4.8 MPa (18% improvement) and split tensile strength of 3.8 MPa (19% improvement). These results confirm the synergistic effect of bacteria and SCMs in enhancing mechanical properties. AF10FA10 exhibited the lowest water absorption and porosity, showing a 7% reduction in water absorption compared to the control. Acid resistance was significantly improved, with AF10FA10 experiencing only an 18% strength loss after 28-day immersion in 2% H₂SO₄, compared to 45% loss in the control mix. This demonstrates superior resistance to corrosive environments. Micro structure analysis confirmed the presence of calcite crystals bridging micro cracks while and detected crystalline calcium carbonate phases, validating the role of microbial calcium precipitation. Porosity reduction and micro crack healing were visible through denser matrix formation and carbonate layer deposition within voids. While AF10FA10 achieved higher compressive strength, its embodied carbon remained comparable to the control mix due to 20% cement replacement with SCMs. Estimated CO₂ emissions were reduced by 15–20%, lowering the effective footprint to ~475–490 kg CO₂/m³ compared to 487.5 kg CO₂/m³ for the control. This demonstrates that performance enhancement can be achieved without increasing environmental burden. Although freeze–thaw resistance testing was not conducted in this study, its importance is recognized and it is recommended for future work as part of a broader durability assessment under aggressive climatic conditions. In summary, the AF10FA10 mix incorporating Bacillus megaterium, Fly Ash and Alccofine offers a holistic improvement in strength, durability, and sustainability. These findings support the feasibility of using microbial-based self-healing concrete for long-lasting, eco-efficient infrastructure. Further field trials and full Life Cycle Assessment (LCA) studies are recommended to validate long-term applicability.

5. BIBLIOGRAPHY

• ^[1] TERMKHAJORNKIT, P., NAWA, T., YAMASHIRO, Y., et al., “Self-healing ability of fly ash–cement systems”, Cement and Concrete Composites, v. 31, n. 3, pp. 195–203, 2009. doi: http://doi.org/10.1016/j.cemconcomp.2008.12.009.
  » https://doi.org/10.1016/j.cemconcomp.2008.12.009
• ^[2] GAVIMATH, C.C., MALI, B.M., MALLPUR, J.D., “Potential application of bacteria to improve the strength of cement concrete”, International Journal of Advanced Biotechnology and Research, v. 3, pp. 541–544, 2012.
• ^[3] SAHOO, S., DAS, B.B., RATH, A.K., et al., “Acid, alkali and chloride resistance of high volume fly ash concrete”, Indian Journal of Science and Technology, v. 8, n. 19, 2015. doi: http://doi.org/10.17485/ijst/2015/v8i19/72266.
  » https://doi.org/10.17485/ijst/2015/v8i19/72266
• ^[4] HARSHALI, J., “Bio concrete and bacteria based self healing concrete”, International Journal of Research in Engineering and Technology, v. 05, n. 05, pp. 95–99, 2016. doi: http://doi.org/10.15623/ijret.2016.0505018.
  » https://doi.org/10.15623/ijret.2016.0505018
• ^[5] KHALIQ, W., EHSAN, M.B., “Crack healing in concrete using various bio influenced self-healing techniques, Construction and building materials”, Construction & Building Materials, v. 102, pp. 349–357, 2016. doi: http://doi.org/10.1016/j.conbuildmat.2015.11.006.
  » https://doi.org/10.1016/j.conbuildmat.2015.11.006
• ^[6] REDHA, A., SANA, M., “Use of bacteria to self- healing concrete cracks”, Diyala Journal of Engineering Sciences, v. 4, pp. 27–36, 2014.
• ^[7] PURNELL, P., “Material nature versus structural nurture: the embodied carbon of fundamental structural elements”, Environmental Science & Technology, v. 46, n. 1, pp. 454–461, 2012. doi: http://doi.org/10.1021/es202190r. PubMed PMID: 22084900.
  » https://doi.org/10.1021/es202190r
• ^[8] MILLER, S.A., JOHN, V.M., PACCA, S.A., et al., “Carbon dioxide reduction potential in the global cement industry by 2050”, Cement and Concrete Research, v. 114, pp. 115–124, 2018. doi: http://doi.org/10.1016/j.cemconres.2017.08.026.
  » https://doi.org/10.1016/j.cemconres.2017.08.026
• ^[9] COPPOLA, L., COFFETTI, D., CROTTI, E., et al., “An Empathetic Added Sustainability Index (EASI) for cementitious based construction materials”, Journal of Cleaner Production, v. 220, pp. 475–482, 2019. doi: http://doi.org/10.1016/j.jclepro.2019.02.160.
  » https://doi.org/10.1016/j.jclepro.2019.02.160
• ^[10] YANG, K.-H., JUNG, Y.-B., CHO, M.-S., et al., “Effect of supplementary cementitious materials on reduction of CO2 emissions from concrete”, Journal of Cleaner Production, v. 103, pp. 774–783, Sept. 2015. doi: http://doi.org/10.1016/j.jclepro.2014.03.018.
  » https://doi.org/10.1016/j.jclepro.2014.03.018
• ^[11] VAGHELA, B., PITRODA, R., ““To investigate the impact of ceramic tile powder on concrete properties”, International Journal of Engineering Trends and Technology, v. 69, pp. 11–16, 2021. doi: http://doi.org/10.14445/22315381/IJETT-V69I8P202.
  » https://doi.org/10.14445/22315381/IJETT-V69I8P202
• ^[12] GAN, V.J.L., CHENG, J.C.P., LO, I.M.C., “A comprehensive approach to mitigation of embodied carbon in reinforced concrete buildings”, Journal of Cleaner Production, v. 229, pp. 582–597, 2019. doi: http://doi.org/10.1016/j.jclepro.2019.05.035.
  » https://doi.org/10.1016/j.jclepro.2019.05.035
• ^[13] RAHLA, K.M., MATEUS, R., BRAGANÇA, L., “Comparative sustainability assessment of binary blended concretes using Supplementary Cementitious Materials (SCMs) and Ordinary Portland Cement (OPC)”, Journal of Cleaner Production, v. 220, pp. 445–459, 2019. doi: http://doi.org/10.1016/j.jclepro.2019.02.010.
  » https://doi.org/10.1016/j.jclepro.2019.02.010
• ^[14] XIAO, J., WANG, C., DING, T., et al., “A recycled aggregate concrete high-rise building: Structural performance and embodied carbon footprint”, Journal of Cleaner Production, v. 199, pp. 868–881, 2018. doi: http://doi.org/10.1016/j.jclepro.2018.07.210.
  » https://doi.org/10.1016/j.jclepro.2018.07.210
• ^[15] GOLEWSKI, G.L., “Green concrete based on Quaternary binders with significant reduced of CO₂ emissions”, Energies, v. 14, n. 15, pp. 4558, 2021. doi: http://doi.org/10.3390/en14154558.
  » https://doi.org/10.3390/en14154558
• ^[16] AHMAD, I., SHOKOUHIAN, M., OWOLABI, D., et al., “Assessment of biogenic healing capability, mechanical properties, and freeze–thaw durability of bacterial-based concrete using Bacillus subtilis, Bacillus sphaericus, and Bacillus megaterium”, Buildings, v. 15, n. 6, pp. 943, Jun. 2025. doi: http://doi.org/10.3390/buildings15060943.
  » https://doi.org/10.3390/buildings15060943
• ^[17] AHMAD, I., SHOKOUHIAN, M., JENKINS, M., et al., “Quantifying the self-healing efficiency of bioconcrete using Bacillus subtilis immobilized in polymer-coated lightweight expanded clay aggregates”, Buildings, v. 14, n. 12, pp. 3916, Dec. 2024. doi: http://doi.org/10.3390/buildings14123916.
  » https://doi.org/10.3390/buildings14123916
• ^[18] AHMAD, I., SHOKOUHIAN, M., JENKINS, M., et al., “Factors influencing bacterial-based precipitation, assessment of crack inducing, durability and characterization methods: a comprehensive review”, Innov. Infrastruct. Solut., v. 10, n. 3, pp. 107, 2025. doi: http://doi.org/10.1007/s41062-025-01912-3.
  » https://doi.org/10.1007/s41062-025-01912-3
• ^[19] IS 2386 (Part I–IV): 1963, Methods of Test for Aggregates for Concrete, Bureau of Indian Standards (BIS), New Delhi.
• ^[20] THAKUR, A., PHOGAT, A., SINGH, K., “Bacterial concrete and effect of different bacteria on the strength and water absorption characteristics of concrete: a review”, International Journal of Civil Engineering and Technology, v. 7, pp. 43–56, 2016.
• ^[21] CHAHAL, N., SIDDIQUE, R., RAJOR, A., “Influence of bacteria on the compressive strength, water absorption and rapid chloride permeability of fly ash concrete”, Construction & Building Materials, v. 28, n. 1, pp. 351–356, 2012. doi: http://doi.org/10.1016/j.conbuildmat.2011.07.042.
  » https://doi.org/10.1016/j.conbuildmat.2011.07.042
• ^[22] GOLEWSKI, G.L., “Combined effect of coal fly ash (CFA) and nanosilica (nS) on the strength parameters and microstructural properties of Eco-friendly concrete”, Energies, v. 16, n. 1, pp. 452, 2022. doi: http://doi.org/10.3390/en16010452.
  » https://doi.org/10.3390/en16010452
• ^[23] GOLEWSKI, G.L., “Fracture performance of cementitious composites based on Quaternary blended cements”, Materials, v. 15, n. 17, pp. 6023, 2022. doi: http://doi.org/10.3390/ma15176023. PubMed PMID: 36079405.
  » https://doi.org/10.3390/ma15176023
• ^[24] AHMAD, I., SHEN, D., KHAN, K.A., et al., “Evaluation of mechanical properties and environmental impact of using limestone powder in high-performance concrete”, Magazine of Concrete Research, v. 74, n. 24, pp. 1280–1295, 2022. doi: http://doi.org/10.1680/jmacr.21.00199.
  » https://doi.org/10.1680/jmacr.21.00199
• ^[25] MOHAMED, H.A., “Effect of fly ash and Fly Ash on compressive strength of self-compacting concrete under different curing conditions”, Ain Shams Engineering Journal, v. 2, n. 2, pp. 79–86, 2011. doi: http://doi.org/10.1016/j.asej.2011.06.001.
  » https://doi.org/10.1016/j.asej.2011.06.001
• ^[26] CHU, H.-H., SIDDIQ, B., ASLAM, F., et al., “Coupled effect of poly vinyl alcohol and fly ash on mechanical characteristics of concrete”, Ain Shams Engineering Journal, v. 13, n. 3, pp. 101633, 2022. doi: http://doi.org/10.1016/j.asej.2021.11.002.
  » https://doi.org/10.1016/j.asej.2021.11.002
• ^[27] KIRAN, T.G.S., RATNAM, M.K.M., “Fly Ash as a Partial Replacement of Cement in Concrete and Durability Study of Fly Ash in Acidic (H2SO4) Environment”, International Journal of Engineering Research and Development, v. 10, pp. 1–13, 2014.
• ^[28] SOUNDHARYA, S., NIRMALKUMAR, K., “Study on the effect of calcite-precipitating bacteria on self-healing mechanism of concrete (review paper)”, International Journal of Engineering Research and Management Technology, v. 1, pp. 202–208, 2014.
• ^[29] KANDASAMY, Y., KRISHNASAMY, M.E., MOONGILPATTI KRISHNASAMY, K., et al., “Investigating the influence of various metakaolin combinations with different proportions of pond ash and Alccofine 1203 on ternary blended geopolymer concrete at ambient curing”, Environmental Science and Pollution Research International, v. 31, n. 54, pp. 62877–62888, 2024. doi: http://doi.org/10.1007/s11356-024-35397-x. PubMed PMID: 39460867.
  » https://doi.org/10.1007/s11356-024-35397-x
• ^[30] DANGI, T., CHAND, J., SHARMA, A., “Forecasting strength characteristics of concrete incorporating nano-silica, alccofine and fly ash as partial replacement of cement using artificial neural network”, Journal of Building Pathology and Rehabilitation, v. 9, n. 2, pp. 107, 2024. doi: http://doi.org/10.1007/s41024-024-00460-0.
  » https://doi.org/10.1007/s41024-024-00460-0
• ^[31] NAVEEN KUMAR, K., DIVAHAR, R., SANGEETHA, S.P., et al., “Enhancing alkaline resistance of concrete using alccofine and metakaolin in mineral admixtures of sustainable development”, European Journal of Environmental and Civil Engineering, v. 28, n. 16, pp. 3749–3769, 2024. doi: http://doi.org/10.1080/19648189.2024.2357676.
  » https://doi.org/10.1080/19648189.2024.2357676
• ^[32] BOOBALAN, S.C., GAYATHRI, V., “A critical review on the Alccofine based concrete”, In: Iterative International Publishers (eds), Futuristic Trends in Construction Materials & Civil Engineering, Volume 3 Book 4, Novi, Michigan, Iterative International Publishers, pp. 152–158, 2024.
• ^[33] SINGH KASHYAP, V., AGRAWAL, U., ARORA, K., et al., “FTIR analysis of nanomodified cement concrete incorporating nano silica and waste marble dust”, IOP Conference Series. Earth and Environmental Science, v. 796, n. 1, pp. 12022, 2021. doi: http://doi.org/10.1088/1755-1315/796/1/012022.
  » https://doi.org/10.1088/1755-1315/796/1/012022
• ^[34] GÜNEŞ, M., YÜCEL, H.E., ÖZ, H.Ö., “Investigation with SEM/EDX, XRD, TGA/DTA and FTIR analyses from a new point of view of the effects on cement mortars of different curing conditions and design parameters”, Omer Halisdemir University Journal of Engineering Sciences, v. 11, n. 3, pp. 713–726, 2022, doi: http://doi.org/10.28948/ngumuh.1051296.
  » https://doi.org/10.28948/ngumuh.1051296
• ^[35] MOLLAH, M.Y.A., HESS, T.R., COCKE, D.L., “Surface and bulk studies of leached and unleached fly ash using XPS, SEM, EDS and FTIR techniques”, Cement and Concrete Research, v. 24, n. 1, pp. 109–118, 1994. doi: http://doi.org/10.1016/0008-8846(94)90091-4.
  » https://doi.org/10.1016/0008-8846(94)90091-4
• ^[36] REN, X., ZHANG, W., YE, J., “FTIR study on the polymorphic structure of tricalcium silicate”, Cement and Concrete Research, v. 99, pp. 129–136, 2017. doi: http://doi.org/10.1016/j.cemconres.2016.11.021.
  » https://doi.org/10.1016/j.cemconres.2016.11.021
• ^[37] SHI, T., GAO, Y., CORR, D.J., et al., “FTIR study on early-age hydration of carbon nanotubes-modified cement-based materials”, Advances in Cement Research, v. 31, n. 8, pp. 353–361, 2019. doi: http://doi.org/10.1680/jadcr.16.00167.
  » https://doi.org/10.1680/jadcr.16.00167
• ^[38] GARCÍA LODEIRO, I., MACPHEE, D.E., PALOMO, A., et al., “Effect of alkalis on fresh C–S–H gels. FTIR analysis”, Cement and Concrete Research, v. 39, n. 3, pp. 147–153, 2009. doi: http://doi.org/10.1016/j.cemconres.2009.01.003.
  » https://doi.org/10.1016/j.cemconres.2009.01.003
• ^[39] TOKURA, T., LIM, J., CHUA, A.M., et al., “Determination of Polymer Type and Content in Concrete Materials by FTIR and TGA”, Advanced Materials Research, v. 1129, pp. 151–158, Nov. 2015. doi: http://doi.org/10.4028/www.scientific.net/AMR.1129.151.
  » https://doi.org/10.4028/www.scientific.net/AMR.1129.151
• ^[40] JAIN, B., SANCHETI, G., JAIN, V., “FTIR analysis of silica fume and iron dust added concrete”, Materials Today: Proceedings, v. 60, pp. 777–781, 2022. doi: http://doi.org/10.1016/j.matpr.2022.04.131.
  » https://doi.org/10.1016/j.matpr.2022.04.131
• ^[41] SINGH KASHYAP, V., AGRAWAL, U., ARORA, K., et al., “FTIR analysis of nanomodified cement concrete incorporating nano silica and waste marble dust”, IOP Conference Series. Earth and Environmental Science, v. 796, n. 1, pp. 012022, Jun. 2021. doi: http://doi.org/10.1088/1755-1315/796/1/012022.
  » https://doi.org/10.1088/1755-1315/796/1/012022
• ^[42] TABET, W.E., CERATO, A.B., JENTOFT, R. “The use of thermogravimetry in quantifying the hydration products in cement-stabilized kaolinite”, In: Brandon, T. L., Valentine, R. J. (eds), Geotechnical Frontiers 2017, Reston, ASCE, pp. 92–102, 2017. doi: doi: http://doi.org/10.1061/9780784480472.010.
  » https://doi.org/10.1061/9780784480472.010
• ^[43] DWECK, J., MELCHERT, M.B.M., CARTLEDGE, F.K., et al., “A comparative study of hydration kinetics of different cements by thermogravimetry on calcined mass basis”, Journal of Thermal Analysis and Calorimetry, v. 128, n. 3, pp. 1335–1342, 2017. doi: http://doi.org/10.1007/s10973-016-6080-8.
  » https://doi.org/10.1007/s10973-016-6080-8
• ^[44] VILLAIN, G., THIERY, M., PLATRET, G., “Measurement methods of carbonation profiles in concrete: Thermogravimetry, chemical analysis and gammadensimetry”, Cement and Concrete Research, v. 37, n. 8, pp. 1182–1192, 2007. doi: http://doi.org/10.1016/j.cemconres.2007.04.015.
  » https://doi.org/10.1016/j.cemconres.2007.04.015
• ^[45] WANG, C., CHAZALLON, C., BRAYMAND, S., et al., “Thermogravimetric analysis (TGA) for characterization of self-cementation of recycled concrete aggregates in pavement”, Thermochimica Acta, v. 733, pp. 179680, Mar. 2024. doi: http://doi.org/10.1016/j.tca.2024.179680.
  » https://doi.org/10.1016/j.tca.2024.179680
• ^[46] PANDIARAJ, K.P., SANKARARAJAN, V., “Experimental analysis on light weight concrete utilizing compost and Ground Granulated Blast Furnace Slag (GGBS): insights into elevated temperature properties through TGA”, International Review of Applied Sciences and Engineering, v. 15, n. 2, pp. 252–259, Jun. 2024. doi: http://doi.org/10.1556/1848.2023.00724.
  » https://doi.org/10.1556/1848.2023.00724
• ^[47] VEMPATI, R.K., RAO, A., HESS, T.R., et al., “Fractionation and characterization of Texas lignite class ‘F’ fly ash by XRD, TGA, FTIR, and SFM”, Cement and Concrete Research, v. 24, n. 6, pp. 1153–1164, 1994. doi: http://doi.org/10.1016/0008-8846(94)90039-6.
  » https://doi.org/10.1016/0008-8846(94)90039-6

Publication Dates

• Publication in this collection
  01 Dec 2025
• Date of issue
  2025

History

• Received
  16 May 2025
• Accepted
  30 Sept 2025