Experimental Study and Analysis of Strength Properties and Sulfate Resistance of Self-Compacting Concrete Using Different Admixtures

Abstract

The strength characteristics and sulfate resistance of self-compacting concrete (SCC) containing Class-F fly ash and metakaolin were investigated in an experimental study. Class-F fly ash and Metakaolin were added in varying proportions to the combinations, from 10% to 25%. The qualities were analyzed and discussed. These included the properties of both fresh concrete (slump flow, L-box, V funnel, and U-box) and hardened concrete (sulfate resistance and compressive strength). Class-F fly ash was used in self-compacting concrete (SCC) formulations, which showed 28-day compressive strengths between 30 and 40 MPa. The compressive strength decreased by 15.28% when cured in a MgSO4 solution as opposed to the control mix cured in water, with values ranging from 24 to 35 MPa. The compressive strength ranged from 34 to 54 MPa after curing in a MgSO4 solution, representing a 15.38% reduction from the control mix that was cured in water.

Introduction

I. INTRODUCTION

Cement-based materials are fundamental in construction and are expected to remain vital in the future, but they face challenges related to productivity, cost, quality, and environmental impact [1, 2, 3]. One promising advancement is self-compacting concrete (SCC), which naturally flows and consolidates under its weight, requiring no additional compaction [4]. SCC overcomes issues associated with traditional concrete, like the need for skilled labor, reinforcing bar arrangements, and pumping limitations due to its high fluidity and resistance to segregation [5]. The idea of self-compacting concrete (SCC) was first proposed by Professor Hajime Okamura in 1986, and a prototype was created by Professor Ozawa in Japan in 1988. Traditional vibrated concrete relies heavily on Ordinary Portland Cement (OPC), leading to increased costs and adverse environmental effects. OPC production generates significant CO2 emissions and kiln dust that can harm the environment and human health [6]. One solution is using industrial by-products like fly ash (FA) and Metakaolin (MK) as mineral admixtures to replace OPC in SCC [7]. Fly ash is a residue from coal combustion, On the other hand, kaolinite clay is heated to create metakaolin, an artificial pozzolana. This approach can reduce material costs and benefit the environment [3].

Despite some research on the effects of FA and MK on SCC properties [5, 6, 8], local acceptance of SCC has been limited, especially in regions with harsh environmental conditions [5]. SCC requires careful study due to its sensitivity to constituent properties, demanding high flow ability and segregation resistance. This study investigates the properties of SCC, comparing control concrete with mixtures that replace cement with fly ash and Metakaolin. The characteristics of freshly mixed concrete (slump flow, L-box, V-funnel and Ubox) and the characteristics of hardened concrete (sulfate resistance and compressive strength) are examined and compared. The SCC exhibited satisfactory slump flows of 600750mm, meeting EFNARC guidelines, with appropriate flow times. The L-box test ensured good resistance to segregation, and U-box measurements indicated proper flowability. All fresh properties aligned with European guidelines [9].

The remainder of the manuscript will discuss the methodology, experiments performed, and results.

II. METHODOLOGY AND EXPERIMENTAL PROGRAM

This section discusses the materials used in an experimental program for testing concrete samples in their plastic stage. The chapter also provides details about mix design and curing procedures. The experiment is centered on assessing the properties of self-compacting concrete both with and without the additional cementing materials of fly ash and metakaolin. The materials used include grade 53 of Ordinary Portland cement, fine aggregate (sand), and coarse aggregate.

The aggregates were appropriately sieved, washed, and dried. Drinking water quality was used for the concrete mix. An admixture called Amglen-N was used, conforming to relevant standards. Class F Fly Ash (FA) and Metakaolin (MK) were employed as mineral admixtures. The process of concrete mixing included the precise weighing of fine aggregates, coarse aggregates, water, cement, mineral admixture, and admixture. Hand mixing was carried out on a non-absorbing platform, starting with thoroughly mixin aggregates, followed by adding cement to achieve a uniform color. Water was added gradually, and casting was performed with different percentages (10%, 15%, 20%, and 25%) of Fly Ash and Metakaolin as replacements for cement. Every mix produced a total of 12 samples, comprising cubes designated for compressive strength assessments at both 7 and 28 days, as well as specimens for evaluating sulfate resistance.

To stop or replenish water loss—which is necessary for the hydration process and, ultimately, the hardening of the concrete—the concrete specimens were cured.

Various tests were conducted on fresh concrete to evaluate specific properties, especially for Self-Compacting Concrete (SCC). SCC is distinct from conventional concrete, and its new properties are crucial for successful placement, focusing on passing ability, filling ability and segregation resistance [10].

1. Slump Flow Test: This test assesses the horizontal free flow of SCC without obstructions. It measures the diameter of the concrete circle, indicating filling ability. A higher slump flow value suggests better formwork-filling ability, with a minimum requirement of 650mm for SCC. It does not indicate the concrete’s ability to pass between reinforcements without blocking.
2. V Funnel Test: This test determines concrete’s filling ability (flowability) with a maximum aggregate size of 20mm. The equipment comprises a funnel with a V shape, and the duration taken for concrete to pass through is recorded. Prolonged flow times may indicate low deformability and elevated interparticle friction.
3. L Box Test: This test evaluates the concrete flow and its susceptibility to blocking by reinforcement. The apparatus is an ’L’-shaped box with a gate and vertical lengths of reinforcement. The ratio H2/H1 assesses passing ability, and T20 and T40 times indicate filling ability.
4. U Box Test: This test evaluates SCC’s filling capacity using a vessel divided into two compartments. Reinforcing bars are installed at the gate. The difference in height between the two sections is measured to assess flow and passing ability
5. Compression Testing Machine (CTM): This examination is conducted on cubic specimens to assess compressive strength at various durations, usually at 7 and 28 days. It is advisable to conduct additional tests at ages like 56 days, 13 weeks, and one year. For early strength assessment, tests can be conducted at 24 and 72 hours.
6. Sulfate Resistance Test: This test assesses the concrete’s resistance to sulfate attack by assessing compressive strength following a 7- and 28-day immersion of the cube in a 5% magnesium sulfate solution.

These tests help evaluate the essential properties of fresh and hardened concrete, with a focus on SCC and its unique characteristics and requirements.

III. RESULTS AND DISCUSSION

This section examines the variables investigated in control concrete and concrete that uses fly ash and metakaolin in place of cement to create self-compacting concrete. Comparisons between the various mixes are provided, along with a discussion of the parameters, which include Slump Flow, L-box, V-funnel and U-box for fresh concrete and Compressive Strength and Sulfate Resistance for hardened concrete.

at 28 days, as depicted in Figure 5. The M25 mix showed the best results for cement replacement with Metakaolin for maintaining sulfate resistance, with a compressive strength of 37.05 N/mm² (1.35% loss) at seven days and 53.30 N/mm² (3.4% loss) at 28 days.

Conclusion

The experimental study evaluated self-compacting concrete’s strength properties and sulfate resistance (SCC) when incorporating fly ash and Metakaolin as mineral admixtures. These admixtures were introduced at different replacement levels, including 10%, 15%, 20%, and 25%. Here are the key conclusions drawn from the test results: For Fly Ash SCC: SCC mixes can be effectively formulated with fly ash replacement levels of up to 25%, and all the fresh concrete properties, including slump flow, V-funnel, L-Box, and U-Box, adhere to EFNARC guidelines. A rise in the fly ash percentage replacing cement (F10, F15, F20, F25) results in a decline in compressive strength. When concrete specimens undergo curing in a magnesium sulfate solution, there is a decrease in strength properties compared to water curing. Nevertheless, this decline in strength properties is alleviated, reducing by up to 1.73% when fly ash is introduced as a cement replacement. For Metakaolin SCC: SCC incorporating Metakaolin exhibits satisfactory workability, with properties falling within the EFNARC guideline range. The concrete’s compressive strength increases by up to 26% as the cement replacement level with Metakaolin rises from 10% to 25%, compared to the control mix. This increase is attributed to the pozzolanic properties of Metakaolin, which react with free lime (calcium hydroxide) in cement to produce additional cementitious compounds. The inclusion of Metakaolin as a cement replacement enhances the sulfate resistance of the concrete. With the replacement percentage reaching 25%, the loss in strength parameters decreases by up to 3.4% compared to the control mix.

References

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Copyright

Copyright © 2024 Mr. Irfan Majeed , Mr. Mir Suhail Ahmed. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.