Lime activated flyash-phosphogypsum blend as a low-cost alternative binder

Abstract

This study investigates the potential of a blended binder formulated from two industrial solid wastes viz. phosphogypsum and fly ash in combination with lime. Three mix proportions of phosphogypsum and fly ash were investigated, and the minimum lime contents required for activation were determined using the Eades and Grim pH test. The lime–fly ash–phosphogypsum blends were then cast into cubes, both in their paste form as well as mortar form, mixed with sand in the ratio of 1:3. They were cured for a period of seven days, and afterwards, their compressive strength was determined. Ordinary Portland cement and lime mortar blocks were also cast as control specimens for comparative evaluation of the strength. The optimal lime–fly ash–phosphogypsum blend was identified and used to construct a masonry prism, and the strengths of the masonry prisms were also evaluated. The optimal lime–fly ash–phosphogypsum blend mortar was also subjected to an X-ray diffraction analysis to determine the reaction products formed during hydration. The study revealed that 5% lime mixed with fly ash:phosphogypsum in the ratio of 3:1 was the optimal proportion which gave the maximum strength to the cubes. The optimal lime–fly ash–phosphogypsum blend mortar developed strength that was higher than conventional Portland cement and lime mortar. The optimal lime–fly ash–phosphogypsum blend mortar masonry prisms developed strength that was comparable to that of Portland cement mortar masonry. The X-ray diffraction analysis revealed the formation of calcium silicate hydrate minerals as well as ettringite and portlandite which were responsible for strength gain.

Lime-Stabilized Solid-Waste Blends as Alternative Building Blocks in Construction

“…This group has the maximum proportion of FA in its blending and hence, the lime requirement for achieving higher strength increases to 6%. A similar increase in lime requirement with the increase in FA content was earlier reported by James et al [25] but in contrast to the work reported by Shen et al [38]. They reported the maximum strength was obtained when the FA/SS ratio was close to 1 whereas in the present study, the maximum strength was obtained when the ratio was 2.…”

“…the work done by Mashifana et al [43] used all the materials that were also a part of the blend in the present study. James et al [25] did not use SS whereas Pai et al [44] did not use PG in their investigations. Figure 8 shows the compressive strengths of the blocks tested in the studies chosen in comparison with the present work.…”

“…Following this, the three different solid wastes were taken in different proportions. The quantity of PG was fixed at 10% as too much PG is detrimental to the development of strength [24,25]. The proportions of FA and SS were varied within the remaining 90% to obtain various mixes.…”

“…Mashifana et al [43] attempted to develop the composite for use in buildings and roads whereas Pai et al [44] investigated the use of the composite as road base material. James et al [25] on the other hand, attempted the use of the composite as a mortar for masonry construction. However, there were some differences in the three studies selected for the comparison despite their similarities to the present study.…”

“…The two best combinations from all the studies have been chosen when a number of combinations tested was more than two. For the purpose of the discussion, the studies carried out by Mashifana et al [43], James et al [25] and Pai et al [44] have been designated as studies 1, 2 and 3, respectively.…”