Study on Development of M20 and M25 Grades of Self Curing Concrete Using Formaldehyde and Sodium Polyacrylate

Abstract

Self-curing concrete, a specialized solution, eliminates external curing for optimal performance in construction. It maintains internal moisture, reducing autogenous shrinkage and early-stage cracking. This innovative approach, promoting sustainable practices, is valuable for high-rise buildings and bridges. Self-Curing properties achieved in concrete through the incorporation of Sodium Polyacrylate and Formaldehyde. Extensive testing was conducted on diverse concrete samples to evaluate their properties, encompassing workability, compressive strength, tensile strength, and flexural strength. Sodium polyacrylate which is a super absorbent polymer is added to the concrete mix of M20 & M25 grade of concrete in variations (0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%) by weight of cement. Formaldehyde added to concrete mix used as shrinkage reducing agent is added 1% with water. Light weight aggregate like brick chips replaced 10% of coarse aggregate are used because bricks absorb and holds a large amount so water. So pre-saturated brick chips are also used to provide internal curing. Sand is replaced by wood powder by 5%, as it also absorbs water. The compressive strength tests were carried out on M20 and M25 grade concretes with different water-cement ratios (for M20 w/c ratio is 0.50 & for M25 w/c ratio is 0.40), adhering to BIS: 516 – 1959 standards. The results indicated that the addition of sodium polyacrylate by weight of cement up to 0.6% led to optimal compressive strength values, beyond which further additions resulted in a decline in strength. Similarly, the split tensile strength tests for M20 and M25 grade concretes showcased the highest values at 0.6% addition of sodium polyacrylate by weight of cement. Subsequent increases in the additive led to a decrease in split tensile strength. Finally, the flexural strength tests for both M20 and M25 grade concretes yielded their highest values at 0.6% sodium polyacrylate by weight of cement, with diminishing flexural strength observed with higher additive percentages. These findings offer valuable insights into enhancing the self-curing properties of concrete and optimizing its characteristics by utilizing sodium polyacrylate as an additive.

Introduction

I. INTRODUCTION

Self-curing is a process in which cement undergoes hydration with the assistance of additional internal water that is distinct from the mixing water. The conventional understanding of concrete curing involves creating conditions that prevent water from evaporating from the surface, essentially curing "from the outside to the inside." On the other hand, internal curing facilitates curing "from the inside to the outside" by utilizing internal reservoirs that have been incorporated into the concrete mixture. These reservoirs are formed with the help of superabsorbent polymers like sodium polyacrylate, saturated wood powder, or lightweight fine aggregates & lightweight coarse aggregate like brick chips. Another term commonly used interchangeably with "Self-Curing" is "Internal-Curing."

II. EXPERIMENTAL MATERIALS

A. Sodium Polyacrylate (SPA)

The use of sodium polyacrylate as a super absorbent polymer in concrete holds up its potential of improving a variety of concrete qualities, including concrete strength.

Properties: -

1. Replacing Portland Pozzolana Cement (PPC) with more sustainable alternatives is a crucial step towards reducing the environmental impact of the construction industry. One such alternative is the use of superabsorbent polymers (SAP), specifically sodium polyacrylate (SPA), which has the remarkable ability to absorb and retain large amounts of water, expanding its volume significantly.
2. In this study, PPC is partially replaced with Sodium Poly-acrylate (SPA) in M20 and M25 concrete mixes at various percentages ranging from 0% to 1% at intervals of 0.2%. The properties of both fresh and hardened concrete are investigated to assess the impact of sodium polyacrylate on concrete performance.

The addition of SPA to the concrete mix leads to several benefits: -

• Increased Workability: The presence of SPA in the mix improves the workability of fresh concrete, making it easier to handle and place during construction.
• Extended Setting Time: The setting time of concrete is increased as the percentage of SPA is increased. This can be advantageous in certain construction scenarios where longer setting times are required.
• Water Retention Capacity: SPA acts as a mini-reservoir, storing significant amounts of water within its structure. During the hydration process, this stored water is gradually released, providing sufficient moisture for cement hydration and promoting proper curing.
• Environmentally Friendly: By adding SPA to PPC cement, we are reducing the requirement of water during hydration process results in self-curing. This ultimately reduces the wastage of water and help in saving environment.  
• Improved Concrete Performance: The presence of SPA can enhance the strength and durability of concrete, especially if proper curing conditions are maintained. While the use of SPA as a cement replacement shows promise in this study, further research and practical application in real-world construction scenarios are essential to fully understand its long-term effects on concrete properties and its potential as a sustainable alternative to PPC. The development and adoption of eco-friendly construction materials and practices are crucial steps towards achieving a more environmentally conscious and sustainable construction industry.

B. Shrinkage Reducing Admixture (FORMALDEHYDE)

When shrinkage-reducing admixtures are introduced during batching, both short- and long-term shrinkage can be greatly reduced. This is realized by addressing the underlying issue that's causing the cement paste's pores and capillaries to shrink as it dries. The specified amount of formaldehyde is added to the water during batching process to reduce shrinkage in concrete.

C. Saturated Light Weight Aggregate

When referring to a set of aggregates with a relative density lower than standard density aggregates (natural sand, gravel, and crushed stone), light weight aggregate is also known as low density aggregate. In M20 and M25 concrete, specified amount of coarse particles are substituted for light weight aggregate (brick-chips).

D. Saturated Wood Powder

A byproduct of furniture and timber manufacturers is wood powder. Also have high water absorption properties which can be used to provide internal water to concrete during the hydration process. A specified amount of fine aggregate is replaced by saturated wood powder. Wood powder is light weight & has the properties to hold water for a long period of time which makes it useful for self-curing.   

E. Cement

Portland pozzolana cement (Fly ash based) of Ultratech, conforming to IS: 1489-1, was the cement used in the experimentation.

III. DESIGN MIX

The mix proportion of M20 & M25 grade of concrete by using Sodium Poly-Acrylate & Formaldehyde is given in Table 5 and Table 6 respectively. The design mix of M20 & M25 grade of concrete by using Sodium Poly-Acrylate & Formaldehyde is shown in Table 7 and Table 8 respectively. The Design mix prepared by IS: 10262-2019.

Conclusion

1) The strength of concrete increased linearly with the increase in addition of sodium poly-acrylate up to 0.6% by weight of cement. On further addition of sodium poly-acrylate the strength starts to decrease. 2) Workability of concrete increases gradually with the addition sodium poly-acrylate due to their large capacity to store water inside it. 3) Self-Curing Concrete shows nearly same strength when compared to the conventional concrete in results that had been drawn from testing. 4) Self-curing concrete is indeed a valuable alternative in regions where water scarcity is a significant concern. Traditional concrete curing methods often involve a substantial amount of water, which can be impractical and environmentally unsustainable in arid or water-scarce areas. Self-curing concrete offers a solution to this problem by reducing the need for external curing and relying on internal mechanisms to maintain adequate moisture levels for proper hydration of the cement. 5) The optimum dosage of sodium poly-acrylate for maximum strength (compressive strength, tensile strength and flexural strength) was found to be 0.6% for the M20 & M25 (with 10% brick-chips replacing coarse aggregate, 5% wood powder replacing fine aggregate, 1% formaldehyde addition to water and 0.6% sodium poly-acrylate added by weight of cement).

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Copyright

Copyright © 2023 Er. Shubham Sharma, Dr. Hemant Sood, Sh. Jasvir Singh Rattan. 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.