This paper presents workability, compressive strength and microstructure for geopolymer pastes and mortars made of class C fly ash at mass ratios of water-to-fly ash from 0.30 to 0.35. Fluidity was in the range of 145–173 mm for pastes and 131–136 mm for mortars. The highest strengths of paste and mortar were 58 MPa and 85 MPa when they were cured at 70 °C for 24 h. In XRD patterns, unreacted quartz and some reacted product were observed. SEM examination indicated that reacted product has formed and covered the unreacted particles in the paste and mortar that were consistent with their high strength.
Belite-rich cement (BRC) can be made at lower temperature, but it has unsatisfactory reactivity. The crystal structure of dicalcium silicate (C 2 S) was modified by solutionizing some additional irons. By adding barium sulfate (BaSO 4 ) in the raw meals, the clinkers were easier to be burnt, and the compressive strength of BaSO 4 -modified BRC was considerably improved. The distortion of the crystal structure of C 2 S was confirmed by the interplanar distance change and nuclear magnetic resonance (NMR) of 29 Si in C 2 S. An effective way was found to activate C 2 S and to broaden the application field of Belite-rich cement.
To investigate the early-age behaviors of concrete under a restrained condition, a set of apparatus was developed. In this way, the tensile creep and other early-age properties can be investigated in depth. By measuring the modulus of elasticity of concrete, synchronous shrinkage of concrete and steel rings and free shrinkage of concrete, the deformations of concrete ring can be quantified respectively. The experimental results show the tensile stress in concrete is time-dependent, and the stress at cracking is much lower than the tensile strength at that age; the tensile creep plays an important role in relaxing the tensile stress and postponing the cracking of concrete.
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