Combined with DTG analysis, X-Ray diffraction analysis （XRD） and field emission scanning electron microscopy analysis （FSEM） affiliated with energy dispersive spectrometer analysis （EDS）, the early hydration and carbonation behavior of cement paste compacts incorporated with 30% of dolomite powder at low water to cement ratio （0.15） was investigated. The results showed that early carbonation curing was capable of developing rapid early strength. It is noted that the carbonation duration should be strictly controlled otherwise subsequent hydration might be hindered. Dolomite powder acted as nuclei of crystallization, resulting in acceleration of products formation and refinement of products crystal size. Therefore, as for cement-based material, it was found that early carbonation could reduce cement dosages to a large extent and promote rapid strength gain resulting from rapid formation of products, supplemental enhancement due to water release in the reaction of carbonation, and formation ofnanometer CaCO3 skeleton network at early age.
This work focuses on the dynamic rheological behavior of low water-to-binder ratio cement mortars blended with fly ash microspheres（FAM） or silica fume（SF）. The initial slump flow of each group has been controlled at similar values by adjusting the superplasticizer dosages. With the help of a coaxial cylinder rheometer, the dynamic rheological behaviors of these mortars are investigated by frequency sweeping in the range of 0-2 Hz under large amplitude oscillatory shear（LAOS）. Based on the systematical elaboration of dynamic rheological testing theory, the experimental data are processed according to Lissajous plot fitting to reveal the viscoelastic characteristics. The nonlinearity of response signals is further assessed with Fourier transform（FT） analysis. The parameters, storage modulus G＇, loss modulus G＂ and relative amplitude I3/I1 are proposed to clarify the influences of FAM and SF on the stability and energy consumption of local structures and nonlinearity of response torques. The hydration characteristics of various groups well confirmed the rheological phenomenon. This study is beneficial for the preparation and optimization of flow state concrete such as pumping concrete and self-compacting concrete.
In order to understand the effect of powders ground from reactive sandstone replacing cement on reducing or suppressing alkali-silica reaction（ASR）, and to identify the mechanism of suppressing ASR by this powders, mortar and paste containing reactive sandstone powders of four replacement levels ranging from 10wt% to 40wt% and four specific surfaces areas ranging from 210 m^2/kg to 860 m^2/kg were studied. The experimental results showed that incorporation of 40wt% reactive sandstone powders could suppress ASR effectively except for mortar containing reactive sandstone powders with specific surface area of 610 m^2/kg, which disagreed with the most results reported that the higher reactive powder specific surface area, the smaller ASR expansion. By means of fl ame photometry, Fourier transform infrared spectroscopy（FT-IR） and thermo gravimetric analysis（TG）, the mechanism of reactive sandstone powders on reducing or suppressing ASR was soluble alkalis type of reactive sandstone powders and the competition of liberating and bonding alkali of cement paste containing reactive sandstone powders,when the ability of alkali bonding was greater than the ability of alkali liberation, ASR caused by reactive sandstone was supressed effectively.
Early hydration mechanism of cement-based materials with silica fume, nano-SiO2 and silica sol of different contents was investigated, and the detailed effect of these Si-rich mineral admixtures in three stages of early hydration（NG, I, D） using kinetics model was focused. The results showed that silica fume, nano-SiO2, and silica sol have significant effect on kinetic parameters n, k1, k2 and k3, the fineness and existing form of SiO2 particles in these Si-rich mineral admixtures are two important factors to affect the hydration process and on the parameters. Through integrated use of methods of hydration heat-Krstulovic-Dabic Modelsynthetical thermal analysis, data of hydration heat were collected, hydration degree was characterized, as well as the resulting crystallization behavior of early hydration, to build a numerical relationship between parameter n and CH contents that n decreases with increasing CH, and thus, a direct connection between hydration heat release behavior and crystallization behavior has been established.
The self-propagating combustion reaction（SPCR）method was employed to synthesize C4AF using metal nitrates as cation precursors and urea as fuel.Thermal decomposition behavior of dried gels,phase identification and crystallinity of synthesized C4AF,and impact of urea to metal nitrates（UR/MN）molar ratio on synthesis effect were investigated with the aid of differential thermogravimetric analysis,X-ray diffraction and Fourier transform inferred spectrometry.It is found that pure C4AF can be prepared by the SPCR method in 2 h at 500℃.The UR/MN molar ratio plays a significant role in the thermal decomposition behavior of dried gel,purity,crystallinity and crystallite size of synthesized C4AF.Ignition temperature should be not lower than 500℃but higher temperatures were unnecessary.No trace of free lime in synthesized C4AF is detected and calcium carbonate is the transition phase.Further calcining the synthesized C4AF at high temperatures is beneficial for increasing crystallinity,purity and crystallite size.Reaction activation energy of the further calcination process is 119.6 kJ/mol.It is more efficient to improve the synthesis effect by increasing UR/MN molar ratio than further calcination at high temperatures.
