Materials Science Forum Vol. 1036

Abstract: The influence of uranium simulated waste water on the hydration properties of the cement was studied by modern test methods such as TAM air, XRD, FTIR, and SEM-EDS. The results show that uranium can promote the hydration of mineral C₃S, and inhibit the hydration of mineral C₃A. By comparing scanning of hydration products, it was found that the existence of uranium significantly changed the morphology of clinker hydration products , but uranium had little effect on the type of clinker hydration product.

Abstract: A gas-solid reaction method was adopted in this work to explore the influence of SO₂ gas on the composition and structure of secondary sintering cement clinker. In this process, the Portland cement clinker was secondarily sintered at different temperatures and a mixed gas mixed with SO₂ was introduced simultaneously in a tube furnace. X-ray powder diffraction (XRD) combined with rietveld refinement was used to determine the phase composition of the cement clinker and the corresponding phase content. The experimental results showed that the increase in temperature conduced to increasing the content of SO₃ solid solution, C₂S and CaO, but decreasing the C₃S content. Moreover, as the ratio of SO₃/MgO (by mass) increases, the content of M1-type alite also increased. And the result of hydration heat release was positively correlated with the content of alite in the clinker. If the content of alite was low, the heat flow was low, as well as the cumulative heat, and vice versa.

Abstract: The self-healing properties of ultra-high toughness fly ash based geopolymer curing in air and water were studied under 2% pre-tension strain. The experimental results show that under these two curing conditions the tensile stress and water absorption of FA-EGC have been recovered and the pore structure has also been improved, indicating that self-healing has taken place in the specimens. Compared to the air environment, the water environment is proved to be a better environment for the self-healing of FA-EGC. It was observed that there were unreacted fly ash particles at the cracks through SEM. And more N-A-S-H gels were found under the water environment, indicating that N-A-S-H gels may enhance the fiber/matrix interface and improve the density of the matrix, resulting in the higher recovery of tensile stress and water absorption.

Abstract: Belite - ye’elimite - ternesite (BYT) cement clinker has attracted much attention due to its advantages of wide range of raw materials, low energy consumption and low carbon emission compared with ordinary portland cement (OPC). In this experiment, chemical reagents were used as raw materials. The effects of calcination temperature and calcination time on clinker synthesis were studied. The best sintering temperature was determined by sintering in rang of 1150-1300°C (setting a temperature point every 30 °C), and then the samples were sintering for 1-6 hours (setting every hour) to determine the best sintering time. The stable condition of the BYT clinker was determined. The phase composition and microstructure of cement clinker were analyzed by X-ray powder diffraction (XRD) Rietveld refinement and Scanning Electronic Microscopy (SEM). The results showed that the desired clinker could be obtained by sintering at 1210°C for 2 hours. In the presence of C₄A₃$, the hydration of C₅S₂$ was accompanied by the formation of gypsum and the precipitation of ettringite.

Abstract: In this investigation, calorimetry, quantitative X-ray diffraction analysis and the scanning electron microscopy were applied to explore the mechanism of hydration modification of cement with diethanol-isopropanolamine (DEIPA). It showed that the addition of DEIPA favoured the strength development on 3 and 28 days, but was undesirable for the 1d strength. The reason for this was that the dissolution of intermediate phase being promoted by DEIPA participated in the aluminate reaction interrupting the normal hydration of C₃S. Appropriate adjustment on SO₃ content in the cement was able to slow down the rate of aluminate reaction allowing C₃S to react in a right fashion, which gave an optimum strength enhancement at early ages. The addition of DEIPA also impacted the formation of hydrates. Significant differences can be recognized in quantities, chemical compositions and the morphologies of hydrates in blank sample and the DEIPA-dosing ones. With the help of SO₃ adjustment in cement with DEIPA, a great number of hydro-sulfoaluminates precipitated at the early stage of hydration to decrease the porosity of hardened cement pastes, which contributed to the strength gain of cement.

Abstract: The use of calcined clay and limestone as supplementary cementitious materials, can have a certain influence on the hydration of Portland cement. This paper reviewed the influence of limestone and calcined clay and the mixture of limestone and calcined clay on the hydration of cement. Both limestone and calcined clay accelerate the hydration reaction in the early hydration age and enhance the properties of cement. Limestone reacts with C₃A to form carboaluminate, which indirectly stabilized the presence of ettringite, while calcined clay consumed portlandite to form C-(A)-S-H gel, additional hydration products promote the densification of pore structure and increase the mechanical properties. The synergistic effect of calcined clay and limestone stabilize the existence of ettringite and stimulate the further formation of carboaluminate, as well as the C-(A)-S-H gel, contributed to a dense microstructure.

Abstract: Calcium aluminate cement (CAC) has excellent resistance to seawater erosion, but the mechanism remains to be explored. Effects of NaCl and CaCl₂ on the hydration of CAC at 5, 20 and 40°C were investigated in this paper by X-ray diffraction(XRD), thermal analyzer(TG-DSC), scanning electron microscopy(SEM), acoustic and electroacoustic spectrometer. Results show that the varieties of chlorides have great impacts on the chloride binding ability, mechanical properties and microstructure of cement pastes at different temperatures. At 5°C and 20°C, the formation of C₂AH₈ is suppressed by chloride attack. Though the addition of NaCl promotes the formation of CAH₁₀, CaCl₂ leads to a denser microstructure and the improvement in compressive strength. At 40°C, C₂AH₈ disappears by chloride attack, while C₃AH₆ and Friedel’s salt increase. Comparing with the attack of CaCl₂, NaCl contributes to the formation of C₃AH₆. Therefore, it results in a the retraction in compressive strength, ascribing to a coarser structure. In addition, although NaCl is superior in chemical binding ability, CaCl₂ has better physical adsorption ability which dominants the binding process, and thus leading to greater amount of bonded chloride than that with NaCl. This research provides the oretical basis for the application of CAC in marine environment.

Abstract: Based on the low-field NMR, this study inveitigated bleeding property of the fresh cement pastes mixed with various gypsum dosage, specific area of cement and water reducers. Results showed that the gypsum dosage between 3 % and 5 % will cause an decrease bleeding and a lower bleeding velocity, while a 1 % gypsum dosage will increase the bleeding as a function of time. The increase of the cement surface will lead to a less bleeding rate. This can be explained that the finer particle will contribute to the packing which will form a low permeability of the cement paste, as a result less bleeding water is observed. The PCEs-made sample has smaller hot zone area which indocated the PCEs has good bleeding stability when varing water cement ratio. Furthermore, bying comparing with the NPE, it was found the ACS type water reducer has higher bleeding sensitivity when high water cement ratios were used.

Abstract: The effects of steel slag with 0, 10%, 20 % and 40% content on the chemical shrinkage, autogenous shrinkage, internal relative humidity, and drying shrinkage of calcium sulfoaluminate cement paste were studied. The results show that the compressive strength of calcium sulfoaluminate cement paste at an early stage decreases gradually when the content of steel slag increases. When the steel slag content is 0 and 10%, the compressive strength of hardened cement pastes gradually decreases at 90 and 180 days, but the samples with steel slag content of 20% and 40% maintain the compressive strength growth within 180 d. With the extension of curing period, the gap of compressive strength is gradually narrowed. The autogenous shrinkage decreases with the increase of steel slag content and has a good linear relationship with the relative humidity inside the paste. The proportion of autogenous shrinkage to chemical shrinkage is deficient, and most chemical shrinkage occurs in the form of the pore volume. Although the trends of drying shrinkage and autogenous are consistent, the former is more severe than the latter.

Abstract: Fly ash is the most common solid waste in the industry, and its high value-added utilization has become a hot issue of study. Carrying out the green synthesis route of zeolite as the raw material of fly ash has become an extremely important scientific significance and practical value. In this paper, the research progress of fly ash-based zeolite was introduced from three aspects, including fly ash activation method, fly ash-based zeolite synthesis method and fly ash-based zeolite in the wastewater treatment sector. The relevant applications of fly ash-based zeolite as an adsorbent material in the treatment of wastewater pollution were summarized, and the development trend has prospected.