There is an increased interest in the reuse of ash waste from biomass combustion, being a sustainable source of energy. This paper investigates the partial replacement of cement and sand in building materials with fly ash waste generated from combustion of woody biomass waste. The results show that the ash widens the particle size distribution of cement and has minerals complementary to portland cement, thus justifying its application as cement replacement, but with a relatively high amount of free CaO and MgO that may exert significant expansion. With ash addition, the rate of hydration, strength, and workability decreased. The optimum dosage showed 15 % of ash, replacing 5 % of cement and 3.33 % of sand, which can still produce a structural grade cementitious material with acceptable workability and mechanical properties. The ash exhibits hydraulic and pozzolanic activity that initially increases and subsequently decreases the amount of Ca(OH) 2 in the hydrated material.

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In this paper the influence of alkali, alkaline earth and transition metals in the form of chlorides salts on the hydration of commercial iron-rich calcium aluminate cement (CAC) is investigated. The effect on setting time and mechanical properties is studied. The results of the setting time obtained from the measured temperature evolution of cement pastes are compared to standard Vicat needle measurements. Addition of alkali metal salts both accelerates the setting time of CAC and deteriorates long-term strengths in the order of decreasing ionic radius of the metals. The effect of alkaline earth metal salts on setting behaviour depends on the amount of addition: low concentrations retard, but high concentrations accelerate setting behaviour. Calcium is found to have the strongest acceleration effect with the lowest deterioration in strength. An interesting regularity is observed when plotting the results of both retarded setting times and strengths against atomic number of added transition metal cation.

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