Strength properties of engineered cementitious composites containing pond ash and steel fiber

ABSTRACT

Concrete technology has seen a recent advancement with the widespread adoption of Engineered Cementitious Composite (ECC). Typically, ECC consist of cement, fly ash, fine sand, fibers, and occasionally other additives or mineral admixtures. However, there has been no exploration into the effects of combining pond ash with steel fibers on emerging cementitious materials like ECC. In this study, seven ECC specimens were made. One was a control mix, and the other six included pond ash with increments of 10% from 10% to 60%. All seven mixes were maintained at a fixed ratio of fly ash 40% and water-to-binder ratio of 0.3. To boost the fresh mix of the ECC mixes, superplasticizer was introduced at a rate of 1% by volume, and steel fiber was incorporated at a rate of 2% by volume of ECC. Addition of pond ash into ECC results exhibits superior properties than control mix.

Keywords:
Engineered cementitious composites; pond ash; fly ash; steel fiber; mechanical properties

1. INTRODUCTION

Engineered Cementitious Composites (ECC) demonstrate superior ductility and demonstrate strain-hardening characteristics [¹,²,³]. In current era, ECC is witnessing increasing adoption in a variety of construction projects, with notable applications encompassing its use in link slabs for bridges, tunnel linings, ECC strips within RC slabs [⁴,⁵,⁶]. ECC mixes incorporate a higher amount of cement content, and this higher cement content can result in environmental impact. Furthermore, ECC excludes the inclusion of coarse aggregate, to preserve the unique qualities of ECC [⁷, ⁸]. ECC results in higher initial costs by the exclusion of coarse aggregate than conventional concrete, which has posed a challenge to the extensive use of ECC [⁹]. In certain scenarios, to decrease the cement volume in ECC, mineral admixtures with pozzolanic properties were added. The inclusion of fly ash content in the ECC mixes enhanced the properties [¹⁰, ¹¹]. In addition to fly ash, various mineral admixtures like GGBS, limestone, and silica fume were assessed for their effects on ECC [¹²,¹³,¹⁴]. Ash into ponds is a significant issue in many developing nations. Therefore, it becomes crucial to identify an alternative for utilizing pond ash [¹⁵,¹⁵,¹⁶,¹⁷]. Efforts were undertaken made to improve ECC behaviour by adding pond ash.

Polyvinyl Alcohol (PVA) [¹⁸], steel [¹⁹], and glass fibers [²⁰] are extensively employed in ECC mortars to augment tensile strength and ductility. ECC with 2% of fiber volume fraction, demonstrates an increased strain hardening from 3% to 7% [²¹, ²²]. Generally, ECC exhibits a strain capability that is 500–600 times greater than traditional concrete [²³,²⁴,²⁵]. The incorporation of randomly oriented discrete fibers into the mix results in ECC that possesses isotropic properties, increased ductility, and enhanced shear capacity. These attributes make it suitable for applications in precast concrete without the need for specialized processing equipment [²⁶, ²⁷].

Based on existing literature, a knowledge gap pertaining to the utilization of pond ash in combination with steel fiber within ECC mixes was identified. Subsequently, this study investigated the effects on pond ash with steel fiber on mechanical properties. Pond ash was added into the ECC mix at varying proportions of 10%, 20%, 30%, 40%, 50%, and 60%, with increments of 10% and its effects on the mechanical properties were studies. The study also examined the correlations between mechanical properties using linear regression analysis.

2. EXPERIMENTAL PROGRAM

2.1. Material used

Cement with high calcium content, along with fly ash and pond ash with low calcium content, and steel fiber are use in this investigation, all sourced from a local supplier. The specific gravity and specific surface area of the Class F pond ash (PA) are 2.17 and 398 m²/kg, respectively [¹⁷]. Chemical proportions of cement, Class F fly ash (FA) and PA are furnished in Table 1. Steel fiber is incorporated into the concrete at a 2% volume fraction in this research and the physical properties of steel fiber is shown in Table 2.

Table 1
Chemical proportions of cement, class F – FA and class F – PA.

S.NO	ELEMENTS	PROPORTIONS (%)
		CEMENT	CLASS F – FA	CLASS F – PA
1.	CaO	62.31	16.15	0.89
2.	SiO2	24.2	42.26	51.4
3.	Al2O3	4.77	26.93	29.2
4.	Fe2O3	3.52	12.82	7.64
5.	SO3	2.59	0.41	4.28
6.	MgO	1.83	0.41	0.52
7.	LOI	0.78	1.02	4.01

Table 2
Physical properties of steel fiber.

FIBERS	DIAMETER (D) µm	LENGTH (L) mm	L/D RATIO	DENSITY g/cm3	NOMINAL TENSILE STRENGTH, MPa	ELONGATION AT BREAK (%)	YOUNG’S MODULUS MPa
Steel	300	12	40	7.9	2000	4.5	175

2.2. Mix proportion

Two types of ECC mixes were prepared: one without pond ash, serving as the control mix i.e., ECC, and others with addition of 10% to 60% pond ash in increments of 10%, are shown in Table 3. A constant ratio of fly ash was maintained across all the mixes. Moreover, the superplasticizer was incorporated to enhance the fresh behavior of ECC. M-sand, which adhered to the standards outlined in zone-III as per IS 383-2016. In the production of ECC cubes, powder ingredients such as cement, Class F fly ash and pond ash, and M-sand are added in the mixer, followed by dry mixing them for a period of three minutes. To improve the workability, the superplasticizer was added in the dry mix. Subsequently, a wet ECC mortar is mixed for another four to five minutes. Afterward, steel fibers are introduced into ECC mortar. Once thoroughly mixed, the ECC mixes are placed into the molds and subjected to 24 hour curing period. Following that, the specimens were immersed in water, and on the 28th day, the evaluation of ECC mortar properties was undertaken using 84 specimens, encompassing shapes such as cubes, dog bone shapes, cylinders, and slabs.

Table 3
Mix proportions of various ECC mixes.

MIX ID	CEMENT	POND ASH	FLY ASH	M-SAND	WATER/BINDER RATIO	SUPER PLASTICIZER (%)	STEEL FIBER VOLUME FRACTION (%)
ECC	1	–	0.4	0.8	0.3	1	2
M1	1	0.1	0.4	0.8	0.3	1	2
M2	1	0.2	0.4	0.8	0.3	1	2
M3	1	0.3	0.4	0.8	0.3	1	2
M4	1	0.4	0.4	0.8	0.3	1	2
M5	1	0.5	0.4	0.8	0.3	1	2
M6	1	0.6	0.4	0.8	0.3	1	2

• ECC: Engineered Cementitious Composites; M1 to M6 – Addition of pond ash with distance of 10%.

2.3. Test methods

2.3.1. Compressive strength

Mortar using dimension of 70.7 mm × 70.7 mm × 70.7 mm was used. The ECC specimen test setup was depicted in Figure 1. The ECC specimen’s strength was assessed using a 2000 kN compressive testing machine after 28-day curing. Load was applied to the specimen in the testing machine at a rate of 140 kg/cm² per minute until the specimen fails. The test results were obtained following the guidelines outlined in IS 516-1959.

Figure 1
Test setup for ECC specimens under compression.

2.3.2. Direct tensile strength

Dog bone mold using size of 350 mm × 60 mm × 30 mm was used. The detail dimension sketch is illustrated in Figure 2. The mold is inserted within the testing apparatus, and subsequently, the apparatus is subjected to a 100-ton capacity load, is indicated in Figure 3.

Figure 2
Dog bone specimen dimension.

Figure 3
Test setup for dog bone specimen.

2.3.3. Modulus of elasticity

After 28 days of curing, ECC specimens with cylinder (Φ-150 mm × L-300 mm) was used, to carried out the modulus of elasticity. Dial gauge is placed in the cylinder, compressometer with a 200 mm gauge length is fitted to the specimen and lastly, the specimen was positioned within the 2000 kN compression testing machine. Test results were taken in accordance with ASTMC469/C469M code.

2.3.4. Impact toughness

The evaluation of ECC mortar impact toughness was conducted using size of (L-600 mm × B- 600 mm × D-100 mm) and the test setup for assessing specimen impact toughness is depicted in Figure 4. A steel hammer rebound was employed, its impacts the center of the slab directly from a height of 1.5 meters, and the test persisted until the specimen failed. Following this, the number of impacts needed to cause the slab failure was examined. Based on these findings, the ECC slab impact toughness was computed.

Figure 4
Test setup of ECC slab specimen.

3. RESULT AND DISCUSSION

3.1. Compressive strength

After 28-day curing period, test was conducted on ECC specimens and the results were displayed in Figure 5. The compressive strength values were as follows: 48.4 MPa for ECC, 49.7 MPa for M1, 51.5 MPa for M2, 52.9 MPa for M3, 51.6 MPa for M4, 51.2 MPa for M5, 50.5 MPa for M6, respectively. The test values clearly demonstrated that the 30% of pond ash exhibits highest strength value. It is concluded that the 30% of pond ash strength exceeds that of the control ECC mix by 9.3%. However, it is noted that the strength value of the mixes gradually reduced by the addition of pond ash exceeds 30%.

Figure 5
Test result on ECC mixes under compressive test.

3.2. Direct tensile strength

ECC mixes including ECC, M1, M2, M3, M4, M5 and M6 displayed tensile strengths of 6.13 MPa, 7.42 MPa, 8.36 MPa, 9.13 MPa, 9.56 MPa, 8.77 MPa, and 7.68 MPa, respectively, at 28 days as depicted in Figure 6. The breaking strengths of ECC can be achieved within the range of 4 to 12 MPa after 28 days (24). The test results indicate that the M4 mix leads to greater strength than all the other mixes. The strength of the M4 mix is discovered to be 56% higher than that of the conventional ECC mix. However, it’s important to note that the strength value of the mix reduced by the addition of pond ash exceeds 40%.

Figure 6
Test result on ECC mixes under direct tensile strength.

To establish the relation between Compressive strength (CS) and direct tensile strength (DTS) was established on ECC specimens using linear regression at 28 days, as demonstrated in Figure 7. The correlation between CS and DTS of ECC specimens, is described by equation (1).

Figure 7
Linear regression formulated between CS and DTS of ECC specimens.

(1) $$\text{CS}=0.\text{7349}\left(\text{DTS}\right)–\text{29}.\text{2}0{\text{R}}^{\text{2}}=0.\text{8389}$$

3.3. Modulus of elasticity

The test results of modulus of elasticity for ECC mixes are illustrated in Figure 8. The modulus results for these mixes after 28 days of curing are as follows: 20.11 GPa for ECC, 20.54 GPa for M1, 21.49 GPa for M2, 22.65 GPa for M3, 21.52 GPa for M4, 21.03 GPa for M5, and 20.69 GPa for M6, respectively. Based on obtained results, it becomes evident that the M3 mix surpasses that of all other mixes, showing a 12.63% increase than the reference ECC mix. However, it is to be noted that the addition of pond ash beyond 30% results in a reduction in the modulus of elasticity.

Figure 8
Test result on ECC mixes under modulus of elasticity.

Furthermore, to establish the relation between the compressive strength (CS) and the modulus of elasticity (ME) of ECC specimens at 28 days, as depicted in Figure 9. The relationship between the CS and ME of ECC specimens, is outlined in equation (2).

Figure 9
Linear regression devised between CS and ME of ECC specimens.

(2) $$\text{CS}=0.\text{5443}\left(\text{DTS}\right)–\text{6}.{\text{516 R}}^{\text{2}}=0.\text{9}0\text{3}$$

3.4. Impact toughness

The ECC mixes recorded rebound counts of 320 for ECC, 336 for M1, 352 for M2, 366 for M3, 354 for M4, 350 for M5, and 342 for M6, respectively, is depicted in Table 4. To calculate impact toughness, multiply the mass of the rebound hammer, the drop height and the number of rebounds recorded. The impact toughness results for mixes are as follows: 27029 N.m for ECC, 28380 N.m for M1, 29732 N.m for M2, 30914 N.m for M3, 29901 N.m for M4, 29563 N.m for M5, and 28887N.m for M6, respectively, at 28 days as shown in Figure 10. These results indicate that incorporation of 30% pond ash enhances the highest toughness than other mixes.

Table 4
Loads on ECC slab with different mixes.

MIX ID	LOADS ON ECC SLAB		HEIGHT, m	REBOUNDS (NUMBER)	IMPACT TOUGHNESS (N m)
	Kgs	N
ECC	5.74	56.31	1.5	320	27029
M1	5.74	56.31	1.5	336	28380
M2	5.74	56.31	1.5	352	29732
M3	5.74	56.31	1.5	366	30914
M4	5.74	56.31	1.5	354	29901
M5	5.74	56.31	1.5	350	29563
M6	5.74	56.31	1.5	342	28887

Figure 10
Impact toughness results of ECC mixes.

4. CONCLUSIONS

The outcomes of research can be formulated in the following conclusions:

1. The M3 mix, incorporating 30% pond ash, displayed maximum compressive strength than the other mixtures. However, when the inclusion of pond ash exceeds 30%, the mechanical properties were gradually reduced for ECC specimens.

2. The inclusion of steel fibers demonstrates a substantial improvement in tensile strength than control ECC mix, attributed to the reinforce the cracks. This remarkable enrichment in direct tensile strength is attributed by the inclusion of steel fibers.

3. Among all the mixes, M3 mix yielding superior strength results in terms of modulus of elasticity and impact toughness.

4. Incorporating pond ash and steel fibers into ECC has the capacity to reduce environmental pollution, enhancing the durability of structures, and consequently lower maintenance and repair expenses.

5. ACKNOWLEDGMENTS

The authors wish to acknowledge Department of Civil Engineering, K.S.Rangasamy College of Technology, Namakkal, Tamil Nadu; Nandha Engineering College, Erode, Tamil Nadu; Surya Engineering College, Erode, Tamil Nadu; K.S.R. College of Engineering, Namakkal, Tamil Nadu for the facility and support extended for the research work.

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Publication Dates

• Publication in this collection
  09 Feb 2024
• Date of issue
  2024

History

• Received
  30 Sept 2023
• Accepted
  03 Jan 2024