Ling Chao Lu

Preparation and Properties of Sulphoaluminate Cementitious Materials with Low Alkalinity

The influence of anhydrite on mechanical property and alkalinity of sulphoaluminate cement clinker was investigated. The alkalinity was examined by mixing powdered samples with a solvent and measuring the pH of the suspension. The hydration mechanism was analysed by XRD analysis. The results indicated that with the increase of anhydrite addition, both the alkalinity and compressive strength decreased. Yeelimite completely converted into ettringite with the dosage of anhydrite reaching to 50% by weight of the paste. With the dosage of 30%, the 7 d pH could be reduced to 10.43 while the 7 d compressive strength was 48 MPa.

Effect of MgO on the Composition, Structure and Properties of Alite-Calcium Strontium Sulphoaluminate Cement

The influence of MgO on the composition, structure and properties of alite-calcium strontium sulphoaluminate cement were investigated by means of X-ray diffraction, SEM–EDS and light analysis. The results show that when the mass fraction of MgO is 1~5%, the early strength of cement can be enhanced significantly. The optimal content of MgO in the cement clinker is 2% and the compressive strengths of the cement at 3, 28 d are 64.3, 103.6 MPa respectively. A suitable amount of MgO can promote the formation of C1.5Sr2.5A3 , while the formation of C1.5Sr2.5A3 can be hindered if the content of MgO is excessive. The existence of MgO can improve the formation of C3S, increasing the mechanical property of the cement. Compared with the Portland cement, alite-calcium strontium sulphoaluminate cement has a higher capacity to dissolve MgO, which indicates that low-quality high-magnesium limestone can be efficiently used in the cement production.

Effect of Sr/Ba Ratio on Dielectric Properties of BSTN Ceramics

The phase composition of (1-x)BaO·xSrO·0.7TiO2·0.3Nb2O5 (BSTN) composite ceramics was analyzed by XRD, and the effect of Sr/Ba ratio on the dielectric properties of BSTN was investigated by impedance analyzer. The results showed that any sample with different x value contained two phases-the perovskite phase and the tungsten bronze phase. The dielectric constants of BSTN basically decreased while the tanδ increased with the increase in x value. Both dielectric constant and tanδ decreased with the applied frequency increased for the same x value. There were two Curie points for BSTN composite ceramics. The first one belonging to the perovskite phase decreased with the increase in x value, but the second one belonging to the tungsten bronze phase kept almost constant at about 300°C.

Preparation and Performance Testing of Foamed Concrete

The key influences of foamed concrete and the optimum preparation technology were studied. The performance of foamed concrete was analyzed by the compressive strength testing, SEM. Results show that the flowability of cement paste is good when water-cement ratio is 0.4. The amount of foam added in sulphoaluminate cement is not able to exceed 3.5L/kg. However, the dilution multiple of foaming agent is near concentration and the mixing time depends on the foam quantity. When the water-cement ratio is 0.4, the foam quantity is 3 L/kg and the foaming agent is diluted 30 times. When the mixing time is 60s, the dry density is around 380kg/m3 and the 7d compressive strength reaches to 0.9MPa.

Effects of Shell and Calcium Carbonate on Properties of Portland Cement

Different amounts of shell and calcium carbonate were added into the Portland cement, their influences on the compressive strength, sulfate corrosion resistance, hydration heat and porosity of the hardened cement paste were studied. Results show that with the increasing of shell content, the compressive strength decreases, however, modest reduction; as the increase of calcium carbonate content, the strength first increases and then decreases, the compressive strength reaches the highest value when the content is 15%. After addition of shell and calcium carbonate, the initial hydration reaction rate accelerates, meanwhile the induction period and acceleration period are brought forward. With the raising of shell and calcium carbonate content, the corrosion resistance coefficient increases gradually, and the sulfate corrosion resistance increases as well. The proportion of the harmless hole which diameter is smaller than 50nm increases after adding the shell and calcium carbonate, it’s beneficial to improve the performance of concrete.

Influence of High-silicon Limestone on Mineral Structure and Performance of Belite-Barium Calcium Sulphoaluminate Clinker

The mineral structure and performance of belite-barium calcium sulphoaluminate cement clinker were investigated by petrographic analysis, X-ray diffraction and scanning electron microscopy, while raw materials were studied by differential thermal analysis, thermogravimetric analysis and X-ray diffraction. The results show that high-silicon limestone has low decomposition temperature which can promote the development of alite by adding small quantity. The formation and development of C3S is hindered in α-quartz while C3S is formed easily by mixing magnesite and dolomite in the low temperature. The proper proportions of high-silicon limestone and ordinary limestone is 1:5, and the compressive of this cement at 3, 7, 28 d are 37.9, 60.3, 87.9 MPa, which shows excellent mechanical properties.

Influences of Microelement on Microstructure and Mechanical Performance of Alite-Strontium Calcium Sulphoaluminate Cement

Alite-strontium calcium sulphoaluminate cement, a new type of cementitious material, is synthesized by combining strontium calcium sulphoaluminate with minerals of Portland cement clinker. The influences of excessive SO3 and SrO on the microstructure and performances of this cement are studied by XRD, SEM-EDS and lithofacies. The results show that the optimal excessive mass fraction of SO3 and SrO are 50% and 80%. The compressive strength of the cement prepared under the testing conditions reaches to 32.8MPa, 66.8MPa and 126.4MPa at 1d, 3d and 28d curing ages, respectively. The additions of SO3 and SrO are benefit to improve the content of strontium calcium sulphoaluminate, and promote the formation of alite at low sintering temperature.

Influence of CaF2 on the Formation Kinetics of Belite-Calcium Barium Sulphoaluminate Cement Clinker

This paper studies the formation dynamics of belite-calcium barium sulphoaluminate cement clinker with and without CaF2. The results suggest that, under the condition of the experimental preparation process, the formation process of belite-calcium barium sulphoaluminate cement clinker is controlled by diffusion mechanism in the temperature range of 1250-1380¡æ and the formation dynamics fits nicely with D4̍́˽̂ځ˿̃˽˸́˽ځ˹2/3=kt. Apparent activation energy was calculated to be 250 kJ·mol-1and 195 kJ·mol-1 for sample clinker without and with 0.6% CaF2 content. It is concluded that CaF2 contributes a lot to the reduction in energy consumption during the process of sintering belite-calcium barium sulphoaluminate cement clinker.

Effect of Water Reducer and Cellulose Ether on Sulphoaluminate Cement-Based Lightweight Thermal Insulation Board

The effects of two admixtures content i.e. water reducer, cellulose ether and water-cement ratio on mechanical strength and dry density of cement-based lightweight thermal insulation board are studied. The result indicates that the water-cement ratio is the important influential factor, which is easier to get good workability. And based on the mechanical strength and dry density, the best range of water reducer content and cellulose ether content are 0.3%-0.6% and 0.4%-0.6% respectively.

Mineral Composition and Performance of Phosphoaluminate Clinker with Addition of SO3

The effect of SO3 on the mineral composition and performance of phosphoaluminate clinker was investigated by means of XRD, IR and SEM. Also, the compressive strength of clinker was performed. The experimental results showed that a certain amount of SO3 would promote the formation of calcium phosphoaluminate mineral, which was good for the strength development of phosphoaluminate clinker. Moreover, the addition of SO3 was benefit to the formation of C4A3 in phosphoaluminate clinker. So, the 5% dosage clinker owns a good strength development.