Replacement of river sand with concrete for environmental factors: its mechanical and microstructural properties

ABSTRACT

Natural sand is a crucial ingredient that is used in cement planning and is also crucial to mix design. This paper examines the fundamental characteristics of concrete that contains both full and partial replacements of natural sand with manufactured sand (M-Sand). In this study, an attempt is made to preserve natural resources like natural sand by partially substituting M-Sand for natural sand. In order to examine the intrinsic characteristics of strength and durability in concrete, samples designated as M1CC, M2CM, M3CSMS, M4CSRS, M5SSRS, and M6SSMS were selected for analysis. A series of experimental assessments were performed to evaluate the compressive strength, split tensile strength, and flexural strength of both conventional concrete and M-Sand concrete within the context of the strength characteristic evaluation. The durability analysis of both conventional and M-Sand concrete was conducted utilizing the sulphate attack test, Acid Attack Test, and the Rapid Chloride Permeability Test (RCPT). Experimental results revealed that concrete with 60% replacement of natural sand by M-Sand exhibited a 20% increase in compressive strength compared to conventional concrete. Durability tests showed a reduction in chloride ion penetration by 25%, and better resistance to acid and sulfate attacks in M-Sand concrete. Morphological analysis indicated that M1CC had higher initial and secondary absorption compared to other specimens, while Scanning Electron Microscopy (SEM) analysis confirmed enhanced microstructural integrity in specimens with optimal M-Sand replacement. These findings demonstrate that partial substitution of natural sand with M-Sand can effectively improve both the strength and durability of concrete.

Keywords:
Manufactured sand; Compressive strength; Acid attack; Sulphate attack; River sand; Microstructure properties; Manufacture sand

1. INTRODUCTION

The rising demand for manufactured sand (M-sand) has emerged due to the dwindling availability of premium natural river sand. Various sized stones are processed through a VSI crusher to produce manufactured sand, which is usually of superior quality and uniform gradation. The M-sand generated from this method often exhibits a coarser texture and a more angular shape. This M-sand is precisely defined in IS 383-1970 under clause 20. The sand is crushed, and the particles are separated by washing them away in a sand trap. When compared to river sand, well-treated M-sand can be utilized to create concrete that offers enhanced durability and mechanical characteristics due to a stronger bond. To evaluate the compressive and flexural strengths of the concrete, silica fume was used to replace a portion of the cement, while M-sand was employed as the fine aggregate. Additionally, this study aims to scientifically compare the influence of synthetic versus natural sand on the respective strength and durability. This paper delves into the durability behavior of both conventional and M-sand concrete after examining the mechanical characteristics of the chosen fine aggregates.

For this operation, natural river sand was used because most governments prohibit dredging of rivers. To address these problems, finding substitute materials is essential. GGBS, Steel slag, Metakaolin, Silica fume, Copper slag, and other industrial by-products are among the compounds that have been identified as potential replacements [¹]. By combining industrial wastes and hybridised fibres to increase the strength and stability of concrete, this study [²] aims to develop healthy, environmentally friendly concrete. To create modified concrete mixes containing 7% silica fume as a cement substitute, steel, basalt, and alkali reactive glass fibers were hybridized in a range of ratios [³]. examines the consequences of partial GGBFS replacement by replacing a portion of the cement in the concrete with GGBFS. In order to meet the increasing demand and shortage of river sand, M-Sand completely substitutes it as a fine aggregate in concrete.

This research explores the potential of substituting river sand with sand derived from waste materials, as suggested in previous work [⁴]. The investigation employs three distinct tree-based algorithms: a single RT model and two ensemble models, namely RF and GBRT, to predict key mechanical properties of concrete made with manufactured sand. Specifically, the study focuses on the UCS and STS of the concrete [⁵]. The aim is to better understand the performance of M-sand in concrete mixes of grades M30 and M65, with experimental analysis conducted on the split tensile strength, flexural strength, and compressive strength of these concrete specimens. This work [⁶] aims to increase the cost- and sustainably-efficientness of the ECM by utilising industrial solid wastes with electrically conductive properties. When building ECM, carbon nanotubes, graphite, and other carbon-based materials are commonly used. A byproduct of the copper industry, copper slag has been evaluated through this research [⁷] as a sand substitute in fibre concrete that also contains 1% hook end steel fibres.

This study investigates the durability, mechanical properties, and chemical composition of high-strength geopolymer concrete (HSGPC) produced with microsilica and a high volume of copper slag. The research also includes a comprehensive review of previous studies that explore the successful utilization of silica fume and copper slag in concrete production, as reported by various researchers. This experimental examination [⁸] looked at a number of durability properties, including compressive and tensile strength of concrete, as well as strength parameters, including capillary suction absorption tests on both conventional concrete and copper slag. The best copper slag concrete mix is employed and compared to ordinary concrete for an economic and ecological inquiry.

This research examines cement pastes incorporating synthetic sand and silica fume, evaluating nine suspension models, which include two liquid thickness models, six relative viscosity models based on solid concentration, and a multilayer perceptron artificial neural network [⁹]. The primary aim of this study is to enhance concrete strength by substituting pozzolanic materials like silica fume, Metakaolin, and GGBS at varying partial cement replacement levels (5%, 10%, and 15%), alongside using M-Sand as a complete replacement for river sand [¹⁰]. Additionally, the study investigates the impact of using synthetic sand and silica fume as partial substitutes for river sand and cement in concrete production. Another key objective is to optimize the properties of silica fume-infused self-compacting concrete (RSCC) to increase its compressive strength compared to conventional concrete, utilizing response surface methodology (RSM) [¹¹, ¹²]. The research also explores the potential of partially replacing river sand with M-sand and incorporating bamboo strips as reinforcement in concrete, enhancing the material’s performance with added cementitious components [¹³]. Furthermore, a study on the use of fly ash concrete (FAC) in M-Sand concrete investigates the effect of varying FAC content (0–100%, with 5% increments) on fresh and hardened concrete properties such as split tensile strength, flexural strength, density, workability, and impact resistance, followed by a microstructural analysis [¹⁴]. Sand mining has significant environmental implications, particularly when excessive extraction disrupts riverine ecosystems, leading to habitat destruction, altered water flow, and increased erosion [¹⁵]. It often causes a decline in aquatic biodiversity, impacts groundwater recharge, and exacerbates riverbank instability, contributing to the depletion of natural resources. The use of manufactured sand (M-sand) as an alternative mitigates these environmental challenges. M-sand, produced from crushed rock, reduces dependency on river sand, conserving vital river ecosystems [¹⁶]. Additionally, it supports sustainable construction practices by minimizing ecological disturbances while ensuring a consistent supply of high-quality sand for industrial use. However, its production requires energy-intensive processes, necessitating a balance to ensure long-term sustainability [¹⁷]. In extreme environmental conditions, M-sand concrete showed promising behavior, particularly in terms of reduced chloride ion penetration (by 25%), and improved resistance to acid and sulfate attacks compared to conventional concrete. These findings suggest that M-sand concrete can withstand harsh conditions, making it a viable option for construction in environments exposed to high levels of moisture, salts, or chemicals [¹⁸].

Six mixes were created in this investigation [¹⁹] with a fixed amount of M sand and varied amounts of dolomite powder. Strength measures were measured after 7, 14, and 28 days [²⁰]. The properties of quarry dust, which is used in concrete, are experimentally studied in this paper [²¹] examines the effects of substituting some of the fine aggregate in concrete for building applications with high-silica sand [²²]. There are four different types of silica sand: VC and TC, which are coarser silica sand, and VF, which is finer silica sand. The purpose of this study [²³] is to investigate the properties of concrete that is created by combining PET and particles of manufactured sand (M-sand) in terms of compressive and tensile strength [²⁴].

2. MATERIALS AND METHODS

2.1. Data materials and sources

The basic raw materials used are cement, water, river sand, M sand, coarse aggregate, fine aggregate and so on. These materials were collected from different areas for research. River sand was gathered from the Vaigai River in Madurai, Tamil Nadu, India, for data collection purposes. Cement is acquired from UltraTech Cement, Mumbai and M Sand was obtained from Alangulam Taluk, Tamil Nadu’s Mahalakshmi Blue Metals & M Sand. SEM results were taken in the place National Lab, Madurai.

2.2. Cement

For this experiment, grade 53 regular Portland cement was sourced locally and tested per IS:4031-1988, meeting IS:12269-1987 standards. Ordinary Portland Cement (OPC) of 43 grade, complying with IS 12269-2013 and ASTM Type I, was used in all mixes. The cement has a specific gravity of 3.15 and Blaine fineness of 350 m²/kg. Ultrafine titanium dioxide nanoparticles (TiO2) and rice husk ash were added as partial replacements for Portland cement. Table 1 summarizes the test results for the cement used.

Table 1
Specific gravity of cement.

TRIALS	Wt. OF EMPTY FLASK (w1)	Wt. OF FLASK + wt. OF SAMPLE (w2)	Wt. OF FLASK + KEROSENE (w3)	Wt. OF FLASK + KEROSENE (w4)	SG (G)
1	0.046	0.079	0.145	0.125	3.12
2	0.046	0.081	0.146	0.125	3.16
3	0.047	0.080	0.145	0.125	3.07

2.3. Coarse aggregate

The machine works with crushed annular granite metal that has an average size of 20 mm as a coarse aggregate. It need to be devoid of organic materials, dust, and clay particles. Table 2 presents the test results for coarse aggregates with varying characteristics. It indicates that artificial sand satisfies the specifications for fine aggregates, including requirements related to gradation, angularity, form, and strength. Manufactured sand fitting the required grade can also be produced. In accordance with IS:383-1970 and the comprehensive examination of sieves provided in the table below, the particle size distribution or coarse aggregate grading revealed approximately an average size of 20 mm.

Table 2
Specific gravity of coarse aggregate.

TRIALS	Wt. OF EMPTY SPECIFIC GRAVITY BOTTLE (w1) (g)	Wt. OF BOTTLE + Wt. OF SAMPLE (w2) (g)	Wt. OF BOTTLE + Wt. OF SAMPLE + Wt. OF WATER (w3) (g)	Wt. OF BOTTLE + WATER (w4) (g)	SPECIFIC GRAVITY (SG) (g/cm3)
1	0.656	1.111	1.799	1.500	2.75
2	0.655	1.105	1.786	1.499	2.72
3	0.656	1.196	1.851	1.500	2.77
			Mean value		2.74

2.4. Fine aggregate

The fine aggregate used in this study was river sand sourced from the Kollidam river near Chidambaram. The sand was found to have a fineness modulus of 2.52 and a specific gravity of 2.23. It was well-graded, meeting the requirements for Zone III as per IS 383-1970.

2.5. Water

There must be no dangerous organic pollutants in the water. Potable water is taken into account for studies as per IS: 456-2000 clause 5.4. Tap water is provided in the Annamalai University structural laboratory, where it has been utilised for concrete construction and specimen curing.

2.6. Ceramic aggregate

Fine aggregate consists of both machine-produced manufactured sand and locally available natural sand. It must be free from organic impurities like silt, clay, and other foreign substances. Table 3 presents the evaluation of various properties of the sand, including bulk density and specific gravity. The study also explored the potential of replacing traditional aggregates with ceramic aggregates, focusing on their impact on the long-term durability of concrete, as outlined in IS:2386-1963. Based on the particle size distribution of the fine aggregate, it aligns closely with the specifications of IS:383–1970, which corresponds to Zone II classification.

Table 3
Specific gravity of ceramic aggregate.

TRIALS	Wt. OF EMPTY SPECIFIC GRAVITY BOTTLE (w1)	Wt. OF BOTTLE + wt. OF SAMPLE (w2)	Wt. OF BOTTLE + wt. OF SAMPLE + wt. of Water (w3)	Wt. OF BOTTLE + WATER (w4)	SG (g)
1	0.474	0.774	1.484	1.301	2.75
2	0.474	0.778	1.495	1.304	2.70
3	0.473	0.830	1.523	1.300	2.72
			Mean value		2.72

2.7. River sand (RS)

The most often used natural material for fine aggregates is river sand, which is considered a natural fine aggregate. However, recent socioeconomic issues have led to a scarcity of this material, which has been a significant issue for the building industry. All of the references for the study use river sand from zone II.

2.8. Manufactured sand (MS)

Fine aggregate was partially substituted with M-Sand. The manufactured sand’s fineness modulus and specific gravity were determined to be 2.73 and 4.66, respectively, and its bulk density was 1.75 kg/m³. It was discovered (Table 4) that the proportion of particles going through different sieves was comparable to that of natural sand.

Table 4
Specific gravity of M-Sand.

TRIALS	Wt. OF EMPTY SPECIFIC GRAVITY BOTTLE (w1)	Wt. OF BOTTLE + wt. OF SAMPLE (w2)	Wt. OF BOTTLE + wt. OF SAMPLE + wt. OF WATER (w3)	Wt. OF BOTTLE + WATER (w4)	SG (g)
1	648	1167	1793	1474	2.595
2	650	1218	1822	1470	2.620
3	649	1152	1796	1481	2.641
			Mean value		2.61

According to Indian Standard Specification, it was tested. The artificial sand that is used comes from a nearby provider. Figure 1 is the image of materials.

Figure 1
Materials used for concrete (a) cement, aggregates, and other materials for concrete mix; (b) fine aggregate (sand) after mixing; (c) cement in its packaged form; (d) combination of cement, sand, coarse aggregates, and other additives.

2.9. Compressive strength test

The intricate examination was meticulously conducted in strict adherence to the guidelines established by IS 516-1959, with the primary objective of accurately assessing the compressive strength of the concrete mixture after a maturation period of 28 days, utilizing a precisely measured concrete cube specimen that boasts dimensions of 150 × 150 × 150 mm. The evaluation process took place utilizing a state-of-the-art compression testing machine, as depicted in Figure 2, which is engineered to handle an impressive maximum load capacity of 2000 kN, thereby ensuring that the test results would be reliable and indicative of the concrete’s true performance under pressure. This comprehensive testing method not only provides critical insights into the durability and structural integrity of the concrete but also contributes significantly to the overall understanding of material properties essential for construction and engineering applications.

Figure 2
Compressive strength (a) specimen; (b) compressive machine.

The compressive strength had been calculated using the following expression

$${\text{f = P/A N/mm}}^{\text{2}}$$

Where,

f = Compressive strength of the specimen in MPa

P = Maximum applied load in N

A = Area of the specimen in mm²

2.9.1. Split tensile test

The tensile strength of the concrete was determined in accordance with IS 5816-1999, using 150 mm diameter and 300 mm height cylinders, as shown in Figure 3. The concrete cylinders were positioned longitudinally between the testing plates and loaded until they fractured into two parts. The tensile strength was then calculated using the following formula:

Figure 3
Split tensile strength (a) specimen; (b) tensile machine.

$$\text{ft = 2P/}\pi \text{DL}$$

where

ft = Splitting tensile strength in MPa

P = Applied load in N

L = Length of the specimen in mm

D = Diameter of the specimen in mm

2.10. Flexural strength test

The test was carried out as per IS 516-1959 to determine the flexural strength (Figure 4) of the concrete at 28 days on 100 × 100 × 500 mm prisms. The test was done on a CTM machine of maximum capacity 1000kN. The appearance of the fractured face of concrete failure was noted. The flexural strength had been calculated using the following expression

Figure 4
Flexural strength (a) specimen preparation; (b) flexural machine.

$${\text{fcr = Pl/bd}}^{\text{2}}$$

where

fcr = Flexural strength in MPa

P = Maximum applied load in N

l = Span length in mm

b = Breadth in mm

d = Depth in mm

2.11. Modulus of elasticity test

The modulus of elasticity of the concrete was determined following the guidelines of IS 516-1959, using 150 mm diameter and 300 mm height cylinders at 28 days, as depicted in Figure 5. The concrete cylinder was placed in an extensometer and positioned in a compression testing machine. Load was applied progressively, with readings taken at each loading stage. The modulus of elasticity was calculated by plotting a graph of stress versus strain values.

Figure 5
Modulus of elasticity (a) concrete cylinder samples prepared for modulus of elasticity testing; (b) compression testing machine used for modulus of elasticity measurement.

2.12. Experimental setup

The chosen concrete mix is used to cast 150 mm × 150 mm × 150 mm cube examples. After that, these cubes are left for 28 days to cure in a curing tank or under other appropriate curing circumstances. The cubes are removed from the curing tank after 28 days of curing and given a 24-hour period to air dry. The cubes’ initial weights are measured and noted after they have dried. Making a Solution of Sodium Hydroxide (NaOH) After adding sodium hydroxide to the necessary amount of water, a 5% sodium hydroxide (NaOH) solution is created. After that, the solution is diluted to make it roughly equal to 13. Using a pH metre or litmus paper, the pH can be changed. Submersion in NaOH Solution The produced NaOH solution is submerged with the cubes. Make sure the cubes’ whole surface is covered in the solution. After being completely submerged, the cubes should be left in the solution for 30 days. Using the test results for compressive strength, beginning weight, and end weight. In Figure 6, specimens are listed.

Figure 6
Specimens immersed in NaOH solution (a) concrete specimens for durability testing; (b) specimens placed in an oven for curing or testing after immersion.

2.13. Mix proportion

In this experiment, the concrete mix design was created explained in Figure 7 in accordance with the given parameters. The mix proportions of concrete (kg/m³) are indicated in Table 5. Concrete mixtures were cast using synthetic sand percentages ranging from 0% to 100% in place of natural sand.

Figure 7
Mixing particles.

Table 5
Mix proportion.

WATER kg/m3	CEMENT kg/m3	M SAND FINE AGGREGATE kg/m3	COARSE AGGREGATE kg/m3	WATER CEMENT RATIO kg/m3
175	389	648	1210	0.45
	1	1.66	3.11	–

2.14. Acid test HCI

Concrete cube samples measuring 150 mm × 150 mm × 150 mm were prepared according to the specified mix proportions, with three cubes cast for each mix.

2.14.1. Salt test (chloride test)

The chloride ion penetration of the concrete mixtures was assessed using ASTM C1202-2012, which measures the electrical conductivity of the concrete after 28 days of curing. Migration cells were constructed using sorptivity samples, with a 0.3 N NaOH solution as the anode and a 3.0% NaCl solution as the cathode. After linking the system, a constant potential of 60 V was applied for six hours to accelerate chloride ingress. The total charge passed through the concrete was monitored for a maximum of six hours, in accordance with the testing protocol.

2.15. Sulphate attack test

Concrete is vulnerable to a complex process known as sulphate attack, which is caused by both physical and chemical salt attacks by sulphates from soil, ocean, or groundwater. Physical salt attack is caused by salt crystallisation. Concrete may expand, lose strength, crack, and disintegrate as a result of sulphate attack.

2.16. Water absorption test

Water absorption is a key factor that impacts the strength and durability of M-sand concrete. In this experiment, the specimens are first placed in an oven and dried at a specified temperature and duration, followed by cooling in a desiccator to prepare for the water absorption test. Once cooled, the samples are immediately weighed. Subsequently, the specimens are immersed in water at a consistent temperature, usually 23°C, for a period of 24 hours or until they reach equilibrium. For instance, the concrete sample is weighed to the nearest 0.1 g. The sample is then submerged in water for 24 hours. After the designated time, the sample is removed from the water, wiped dry with a cloth, and weighed again to the nearest 0.1 g. The study also highlighted that M-sand with higher initial and secondary absorption rates can affect the concrete’s performance by increasing porosity and reducing bond strength between the aggregates and the cement matrix. This could result in weaker concrete with lower durability. Higher water absorption can lead to increased water demand in the mix, which may negatively impact workability and reduce the overall compressive strength. Therefore, managing the water absorption of M-sand is crucial for achieving optimal strength and durability, and selecting M-sand with low absorption is recommended for concrete mixes.

3. RESULT AND DISCUSSION

Determining exposure circumstances is the first step in specifying a durable concrete. Concrete is said to be durable if it can function well under exposure conditions for the desired amount of time while requiring the least amount of maintenance. The durability of concrete is significantly influenced by the environment to which it is exposed. This is a two-phase experimental inquiry. The investigation’s initial stage entailed optimising the replenishment of M-sand. The durability of concrete, including sulphate and acid attack, is covered in the second phase.

3.1. Acid attack test

Concrete’s acid resistance was investigated by submerging the samples in an acidic solution.The test has been run on both standard concrete and concrete specimens that have 60% M-sand instead of fine aggregate. The 150 × 150 × 150 mm specimens were cured in water for a duration of 28 days after casting. In order to remove any loose debris and weak reaction products, the specimens were removed from the curing tank after a 28-day curing period and their surfaces were carefully cleaned with a soft nylon brush. The specimens were weighed initially, submerged in a 5% sulfuric acid solution for the following 28 days, and then their compressive strength was measured. The findings were compared to those of concrete specimens that were not exposed to acid attack. Table 6 tabulates the results.

Table 6 shows the % weight loss and compressive strength loss due to acid assault during a 28-day curing period in sulfuric acid. Compared to concrete samples that contain 60% manufactured sand, samples that use 100% natural sand exhibit significant weight loss and compressive strength loss. When compared to other grades, the M50 grade of concrete shows the lowest percentage of weight loss and compression strength loss, according to the data shown in Figure 8. Additionally, M50 concrete that contains 60% M-sand instead of fine aggregate is more resistant to acid attack than regular concrete.

Table 6
Acid attack test.

MIX cc	BEFORE ACID wt. AT 28 DAYS	AFTER ACID wt. AT 28 DAYS	% LOSS IN wt.
Cube 1	8.713	8.551	1.86%
Cube 2	8.751	8.583	1.91%
Cube 3	8.805	8.644	1.82%
MIX	BEFORE ACID CURING wt. OF CUBES AT 28 DAYS	AFTER ACID CURING wt. OF CUBES AT 28 DAYS	% LOSS IN wt.
Opt. mix 1 cc	8.756	8.592	1.87%
Opt. mix 2 ccm	8.825	8.698	1.43%
Opt. mix 3 (C.S + M.S)	8.913	8.826	0.97%
Opt. mix 4 (C.S + R.S)	8.895	8.787	1.21%
Opt. mix 5 (S.S + R.S)	8.842	8.739	1.16%
Opt. mix 6 (S.S + M.S)	8.9	8.81	1.01%

Figure 8
Weight loss under acid attack.

3.2. Sulphate attack test

Through the immersion of the specimens in sulphate solution, the sulphate resistivity of concrete was investigated. In order to conduct the test, both ordinary concrete and concrete specimens containing 60% M-sand in place of fine aggregate were used. The 150 × 150 × 150 mm specimens were cured in water for a duration of 28 days after casting (Figure 9). After 28 days of curing, the specimens were removed from the curing tank and their surfaces were scrubbed to remove any loose materials and weak reaction products using a soft nylon brush. Following initial weight measurements and a 28-day immersion in a 5% sodium sulphate solution, the specimens’ compressive strength was evaluated and compared to concrete specimens that had not been exposed to an acidic environment.

Figure 9
Weight loss under sulphate attack.

Following a 28-day curing period in sulfate solution, Table 7 shows the percentage of loss of weight and compressive strength loss associated with sulphate attack. Compared to concrete samples that contain 60% manufactured sand, samples that use 100% natural sand exhibit considerably more reductions in weight and compressive strength loss.

Table 7
Sulphate attack test.

MIX	% LOSS IN WEIGHT	% LOSS IN STRENGTH
Opt. mix 1 cc	1.46%	3.22%
Opt. mix 2 ccm	1.32%	2.98%
Opt. mix 3 (C.S + M.S)	0.89%	1.46%
Opt. mix 4 (C.S + R.S)	1.11%	1.72%
Opt. mix 5 (S.S + R.S)	1.24%	2.21%
Opt. mix 6 (S.S + M.S)	0.97%	1.58%

3.3. Water absorption test

The sorptivity, or rate of water absorption, of the exterior and interior concrete surfaces is ascertained by the water absorption test. In this test, the mass gain of concrete samples due to water absorption is measured as a function of time when the specimen is just partially submerged in water. According to the maritime code BS 6349, water absorption, when evaluated in compliance with BS 812-2, should not above 3%. In severe circumstances, such as very aggressive chloride or freeze-thaw exposure, the limit is 2%. For six days, the specimens were kept in a vented oven with a temperature control of 100°C. After removing them, they were weighed. After that, the specimens were kept for a day in a control room with a constant temperature of 20°C and 50% relative humidity. Once again, the specimens were weighed, and the results were used as a benchmark for the water absorption given in Table 8.

Table 8
Water absorption test.

MIX	WATER ABSORPTION OF CUBES AFTER 28 DAYS	POROSITY OF CONCRETE AFTER 28 DAYS
Opt. mix 1 cc	0.52%	1.08%
Opt. mix 2 ccm	0.48%	1.02%
Opt. mix 3 (C.S + M.S)	0.31%	0.64%
Opt. mix 4 (C.S + R.S)	0.38%	0.82%
Opt. mix 5 (S.S + R.S)	0.41%	0.88%
Opt. mix 6 (S.S + M.S)	0.36%	0.73%

3.4. Porosity test

Concrete’s rate of water absorption is computed using porosity testing. Concrete’s porosity is a measurement of its void volume. The rate at which moisture permeates concrete under pressure gradients is known as permeability. Moisture cannot pass through voids unless they are connected and a specific size.

3.5. Water absorption and porosity

Opt. Mix 1 cc

Weight of saturated specimen after 28 days curing, A = 8.798 kg

Weight of dried specimen after 24 days b = 8.754 kg

$$\begin{array}{l}\text{Water absorption \% = A - B/B}\\ \text{=}\text{8}\text{.798 - 8}\text{.754/8}\text{.754 * 100}\\ \text{= 0}\text{.502\%}\end{array}$$

Porosity for Opt. Mix 1 cc

Dry weight A after 28 days curing = 8.788 kg

Weight of specimen after kept in boiling water = 8.818 kg

Apparent weight of specimen in water D = 5.126 kg

$$\begin{array}{l}\text{Volume of permeable voids \% = C - A/C - D * 100}\\ \text{= 8}\text{.818 - 8}\text{.778/8}\text{.818 - 5}\text{.126 * 100}\\ \text{= 1}\text{.08\%}\end{array}$$

3.6. Salt attack test (chloride attack)

A sample of the concrete is ground into a fine dust for the test, any chloride present is then extracted using hot, diluted nitric acid, and any remaining chloride is precipitated with the addition of silver nitrate solution. Here, the passive layer enclosing the steel reinforcement might be attacked by the chloride ions diffusing through the pores in the concrete, resulting in corrosion. To assess the risk of corrosion of the reinforcing concrete in chloride-contaminated concrete, the concentration of chloride is measured at different depths. The concrete’s weight loss and strength loss are displayed in Table 9.

Table 9
Chloride attack test.

MIX	LOSS IN WEIGHT %	LOSS IN STRENGTH %
Opt. mix 1 cc	1.97%	3.78%
Opt. mix 2 ccm	1.78%	3.44%
Opt. mix 3 (C.S + M.S)	1.13%	2.52%
Opt. mix 4 (C.S + R.S)	1.32%	2.86%
Opt. mix 5 (S.S + R.S)	1.68%	3.12%
Opt. mix 6 (S.S + M.S)	1.26%	2.68%

3.7. Results of compressive strength

For six different mixes, the cube compressive strength of both replacement and traditional concrete was measured. When compared to traditional concrete, it was shown that at 28 days, strength increased in all of the mixes. The compressive strength (Table 10 and Figure 10) of M-sand is higher than that of natural river sand when copper slag is replaced with 30% and steel slag with 40%. Concrete’s strength is increased and the cohesiveness of the cement matrix is improved by the angular shape of the copper slag with GGBS. Active C2S and C3S found in steel slag can aid in the hydration process and increase the strength of concrete.

Table 10
Compressive strength result.

MIX	COMPRESSIVE STRENGTH N/mm2
M1CC	44.79
M2CCM	47.95
M3	56.63
M4	54.10
M5	51.92
M6	54.71

Figure 10
Graph of compressive strength.

3.8 Results of split tensile strength

This test measures the tensile strength (Table 11 and Figure 11) of cylindrical specimens indirectly. When steel and copper slag are added to concrete as fine aggregate, the concrete’s split tensile strength is increased in comparison to regular concrete. M-sand exhibits significantly higher strength than natural river sand when 40% of the copper slag and 30% of the steel slag replacement are used. Because steel slag is rougher on the outside than natural sand, it bonds to cement paste more strongly.

Table 11
Split tensile strength result.

MIX	SPLIT TENSILE STRENGTH N/mm2
M1CC	4.8
M2CCM	5.12
M3	5.68
M4	5.13
M5	5.10
M6	5.26

Figure 11
Graph of tensile test.

3.9. Results of flexural strength

A material’s elasticity refers to its capacity to withstand deformation when subjected to force. To determine the load at which the concrete members may crack, the flexural strength must be determined. When copper slag and steel slag were substituted for river sand and M-sand, the flexural strength (Modulus of rupture) increased somewhat. Flexural strength rises as copper and steel slag percentages in fine aggregate reach 40% and 30%, respectively. After 28 days of curing, the increase in flexural strength (Table 12 and Figure 12) is roughly 19% for copper slag and 17% for steel slag.

Table 12
Flexural strength result.

MIX	FLEXURAL STRENGTH N/mm2
M1CC	5.68
M2CCM	6.33
M3	6.79
M4	5.82
M5	5.75
M6	6.66

Figure 12
Flexural strength test.

3.10. Elasticity modulus of concrete results

The elastic modulus of the tested specimens can be determined using the stress-strain curve. Concrete containing 40% copper slag and 30% steel slag exhibited a slight increase in elastic modulus, with values 21.92% and 19.28% higher than those of conventional concrete. This enhancement is likely due to the high angularity of the copper and steel slag, which may have improved the particle-cement paste bond strength (refer to Table 13 and Figure 13).

Table 13
EC concrete results.

MIX	EC FOR CONCRETE × 103 N/mm2
M1CC	29.3
M2CCM	31.24
M3	35.74
M4	34.69
M5	33.75
M6	34.95

Figure 13
EC modulus test.

3.11. Sorptivity test

One type of unidirectional absorption test is the water sorptivity test that given in Table 14 and Figure 14. To evaluate the water absorption rate through capillary rise, a 68-mm-diameter core is coated with epoxy around its perimeter and then positioned in a tray containing a water and Ca(OH)2 solution.

Table 14
Sorptivity test.

M1CC		M2CM		M3CSMS		M4CSRS		M5SSRS		M6SSMS
S^1/2	I (mm)	S^1/2	I (mm)	S^1/2	I (mm)	S^1/2	I (mm)	S^1/2	I (mm)	S^1/2	I (mm)
0	0.00	0	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
8	0.10	8	0.14	7.75	0.04	7.75	0.05	7.75	0.05	7.75	0.04
17	0.18	17	0.27	17.32	0.11	17.32	0.10	17.32	0.11	17.32	0.08
24	0.24	24	0.34	24.49	0.19	24.49	0.17	24.49	0.17	24.49	0.12
35	0.33	35	0.41	34.64	0.26	34.64	0.25	34.64	0.22	34.64	0.17
42	0.47	42	0.46	42.43	0.33	42.43	0.34	42.43	0.29	42.43	0.24
60	0.65	60	0.53	60.00	0.45	60.00	0.41	60.00	0.36	60.00	0.29
85	0.82	85	0.56	84.85	0.52	84.85	0.48	84.85	0.45	84.85	0.38
104	0.90	104	0.60	103.92	0.56	103.92	0.55	103.92	0.54	103.92	0.46
120	0.96	120	0.66	120.00	0.59	120.00	0.60	120.00	0.61	120.00	0.54
134	0.99	134	0.71	134.16	0.61	134.16	0.63	134.16	0.70	134.16	0.60
147	1.00	147	0.73	146.97	0.63	146.97	0.67	146.97	0.75	146.97	0.65
304	1.02	304	0.84	315.31	0.66	315.31	0.71	293.94	0.79	293.94	0.69
440	1.04	443	0.93	431.28	0.67	431.28	0.72	415.69	0.86	415.69	0.72
518	1.06	520	0.95	523.35	0.68	523.35	0.73	509.12	0.87	509.12	0.72
657	1.07	658	0.96	658.18	0.69	658.18	0.74	658.18	0.87	658.18	0.72
726	1.08	727	0.97	726.76	0.69	726.76	0.74	726.76	0.87	726.76	0.72
789	1.09	789	0.97	788.80	0.69	788.80	0.74	788.80	0.87	788.80	0.72

Figure 14
Sorptivity test.

$$\text{I = S · t 1/2}$$

where t is the exposure period (s), S is the sorptivity (m/s1/2), and I is the volume of water absorbed per unit cross section (m). The gravimetric method makes it simple to calculate the amount of water absorbed, but it is not able to watch the water flow and gauge the depth of penetration. The purpose of this test is to find out how susceptible unsaturated concrete is to water seeping through. It gauges how quickly liquids, such as water, are absorbed.

3.12. Microstructural investigation

The interfacial transition zone’s condition was tracked by taking pictures at 10k magnification levels. As shown in Figure 15, the concrete mixtures were created by substituting 10% silica fume for cement, 80% combination for ceramic waste aggregate, and conventional concrete for cement. There isn’t any additional evidence of line cracking between the aggregate and matrix. The information on hydration products and enhanced bonding at the interfacial transition zone is also clearly visible in the magnification photos. The binding of the cement matrix was quite strong due to the presence of C-S-H. Information about the material’s microstructure can be obtained by analysing the damaged specimen using scanning electron microscopy. This helps us to comprehend the visible changes, microscopic cracks, and cavities in the microstructure of the CSH gel and aggregate contact.

Figure 15
SEM analysis.

4. CONCLUSION

In this research, the long-term durability of M-sand concrete was assessed using various durability tests, including the Rapid Chloride Permeability Test (RCPT), Sulfate Attack Test, and Acid Attack Test. These tests were designed to evaluate the concrete’s resistance to chloride ion penetration, acid corrosion, and sulfate-induced degradation over time. By examining these factors, the study assessed how M-sand concrete performs under sustained exposure to aggressive environmental conditions, which is critical for understanding its suitability in real-world applications. According to the current study’s findings, partially substituting M-sand for fine aggregate improves concrete’s performance in the acid attack, compressive, sulphate, chloride, and water absorption tests. Regardless of the grade of concrete with M1CS, M2CM, M3CSMS, M4CSRS, M5SSMS, and M6SSRS, the percentage weight loss owing to sulphate attack is 1.8% for conventional concrete and 1% for concrete substituted with M-sand. For concrete without M-sand replaced, the percentage weight loss owing to acid attack is 2%, while it is 2.65% for ordinary concrete. When it comes to resistance to acid and sulphate assault, M-sand concrete is less durable than regular concrete. The concrete mix’s 28-day compressive strength yielded 63.56 N/mm when 100% of the river sand was replaced with M-sand. Therefore, this study’s findings suggest that M-sand can be used in place of river sand, achieving sustainability in the process. The microstructural analysis i.e., SEM test were conducted to find the exact structure of the specimen content to know the better results. This study highlights the practical benefits of using manufactured sand (M-Sand) as a partial replacement for natural sand in concrete, addressing resource conservation and sustainability. Results show that concrete with 60% M-Sand replacement exhibits a 20% increase in compressive strength and improved durability, with a 25% reduction in chloride ion penetration and better resistance to acid and sulfate attacks. These findings suggest that M-Sand can be an effective, environmentally friendly alternative to natural sand, offering enhanced performance and durability in concrete, making it suitable for construction in harsh conditions while reducing the environmental impact of sand mining.

4.1. Future recommendations

Future research on M-sand should focus on its long-term performance and broader applications in concrete formulations to enhance its adoption in sustainable construction. Key areas include evaluating durability under varying environmental conditions, such as resistance to carbonation, chloride ingress, and freeze-thaw cycles, and studying its compatibility with chemical and mineral admixtures like fly ash and superplasticizers. Investigations into its suitability for high-performance concrete, including self-compacting, high-strength, and fiber-reinforced varieties, can expand its use in advanced construction. Additionally, lifecycle assessments of M-sand production, including its carbon footprint and energy consumption, will provide insights into its environmental and economic benefits compared to river sand, fostering innovation in eco-friendly building materials.

5. Limitations

The study on partial replacement of natural sand with M-Sand in concrete presents some limitations. First, the experimental scope is limited to a specific range of M-Sand replacement levels (up to 60%), and the long-term effects of such replacements on concrete performance are not fully explored. The study also primarily focuses on compressive, tensile, and flexural strengths, without considering other potential critical factors such as shrinkage, thermal properties, or workability variations. While the durability tests demonstrate positive outcomes in terms of chloride ion penetration, acid, and sulfate resistance, the study does not account for the environmental and economic impacts of widespread M-Sand usage, such as its availability and cost-effectiveness compared to natural sand. Additionally, the SEM analysis offers valuable microstructural insights but lacks in-depth exploration of the behavior of M-Sand under different environmental conditions over time. Since the study doesn’t account for regional variations in M-sand quality, construction professionals should implement a localized quality control system for M-sand. This could involve sourcing M-sand samples from different production locations and conducting detailed tests to evaluate their properties such as gradation, shape, texture, and water absorption. A localized database of M-sand quality would help in making informed decisions about M-sand selection and mix design, ensuring that each batch of concrete meets the desired performance criteria.

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Publication Dates

• Publication in this collection
  17 Feb 2025
• Date of issue
  2025

History

• Received
  23 Sept 2024
• Accepted
  09 Dec 2024