Effects of pozzolan waste on hydration and performance of Portland cement and foam glass based plaster

Abstract

Light plaster with expanded aggregates has gained popularity for its durability and light weight. The paper describes the use of expanded glass EG) manufacturing by-product – a mix of metakaolin and glass (M) – and catalyst (K) from crude oil cracking to improve the properties of lightweight plaster with expanded glass aggregate and to reduce the amount of waste in landfills. Mixes with and without EG containing two types of waste were tested by calorimetry methods (V/K=0.35, 72 h). Calorimetry techniques were also used to test the mixes containing melamine based superplasticizer (SP). The following trends were observed through the analysis of calorimetry curves: 1. K (9%) causes earlier hydration of cement but the amount of released heat is lower compared to the control specimen. A sharp initial (humidification) heat release was observed in mixtures with K admixture. 2. M (9%) has insignificant effect on cement hydration. The amount of heat released in the initial stage is similar to that of control specimens and the total amount of released heat is close to the amount released by specimens with K admixture. 3. In specimens containing the mix of by-products (4.5% of each type) the hydration process slows down and the lowest amount of heat is released. 4. In specimens with SP, the total amount of released heat reduces in mixes of all compositions, the period of cement induction is prolonged and the second peak of heat release is delayed compared to the specimens without SP. Tests of mechanical properties revealed that in specimens where part of cement is replaced with the by-products mentioned above (when they are used separately), the compressive strength increases up to 20% after 28 days of curing. However, the compressive strength reduced insignificantly in specimens containing the mix of by-products (4.5% of each type) compared to the control specimen. SEM tests revealed good cohesion between EG and cement matrix. Intensive growth of crystals, especially ettringite, was observed next to EG. The cohesion improves even more when SP is used (the structure of smaller crystals becomes denser). The analysis of SEM results revealed that K and M act as crystallization centres. Cement crystals were observed to enter glass granules through the surface defects and grow inside the granule. Specimens containing M and K mixture had the most porous structure and the weakest cohesion.