It is often necessary to improve the strength of fly ash to enable its use for many geotechnical applications. Lime in some form or other is normally used as an admixture. Methods are established to determine the optimum lime content for fly ash, as the addition of lime beyond the optimum lime content may not be beneficial or economically viable. This paper examines the use of sodium salts to enhance the effect of lime on fly ash. Based on unconfined compression strength tests on a compacted fly-ash–lime–salt specimen, it has been shown that sodium salts improve the strength of a fly-ash–lime mixture. The improvement is salt-specific. This improvement in strength can be attributed to the formation of a greater volume of sodium calcium silicate hydrate gel as opposed to a calcium silicate hydrate. The improvement in strength is greater for sodium hydroxide than for sodium chloride. The increased pH with sodium hydroxide dissolves more silica and can produce more cementitious compounds after reaction with lime. Although sodium sulphate increases the strength initially, its long-term effect is suspect.

In India, it is estimated that 250 billion bricks are produced annually in about 100,000 kilns present all over the country. Mainly due to inefficient production processes, most of the blocks manufactured are of inferior quality, which ultimately becomes a significant source of waste production. The characteristics of Construction and Demolition wastes (C&D) are difficult to predict, but a considerable component of this type of solid waste comprises of bricks in masonry work. As more and more civil structures are nearing the end of their expected lifespan, proper management and disposal of C&D wastes are necessary to obtain a sustainable environment. Ground waste clay brick is a prospective pozzolanic material due to dehydroxylation of clay minerals during its manufacturing process at temperatures between 450°C and 700°C, leading to the disintegration of crystalline phases and formation of reactive anhydrous amorphous phases. A review of the existing literature regarding the use of crushed brick powder (CBP) from waste bricks as well as demolition debris as a supplementary cementitious material has been conducted. It has been observed that the pozzolanic character of clay used for making brick comes from calcining it at an optimum temperature, which is different for different clays. Cement replacement by CBP in concrete mostly causes increased compressive, flexural, and split – tensile strength at 28 and 90 days, indicating good pozzolanic behaviour. 10 – 25% replacement by CBP gives acceptable values of Strength Activity Index (SAI) at 7 and 28 days. Pore refinement causing the formation of additional hydration products due to pozzolanic reaction as well as filler effect of CBP are the primary factors causing improved durability of concrete. Limited research has been done on the effect of the chemical composition of raw clay on the pozzolanic potential of CBP. Future scope in this area can be on enhancement of pozzolanicity in CBP, the study of high volume replacement of CBP in concrete, and the effect of CBP replacement on corrosion of rebar.

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This paper studies the pozzolanic performance of Crushed Brick Powder (CBP) obtained by grounding under- burnt waste bricks from a continuous brick kiln. Two different size fractions of CBP considered for cement replacement are CBP1 passing through 150 μm but retained on 75 μm and CBP 2 passing through 75μm. The compressive strength tests on mortar with CBP reveal that strength does not exceed the control; however, 10 - 15% cement replacement by CBP is optimum. A study of the presence of hydrate phases by XRD and quantification of portlandite in the paste samples by TGA up to 90 days confirms the action of pozzolanicity. Further, To determine the feasibility of CBP1 and CBP2 fractions in concrete, M25 grade concrete's strength and carbonation were studied by replacing 45% cement with a combined proportion of CBP1 (20%) and CBP2 (25%). This replacement reduced the concrete grade from M25 to M20 and increased the accelerated carbonation depth. Despite this, the projected natural carbonation coefficient with accelerated carbonation data is determined as low. The utilised CBP is cost-effective as it requires less mechanical processing and is without any chemical activation, and thus it can satisfactorily be used for low-cost housing construction and lower-grade structural and non-structural uses.