Advanced Materials Research Vols. 168-170

Abstract: To prepare the concrete of high strength and high fluidity, some important factors were investigated, namely species of phosphate, the ratio of phosphate and magnesia, the surface area of phosphate cement, fineness of sand, particle size distribution of coarse aggregate and the ratio of phosphate cement and aggregate. Results showed that the fluidity and strength of phosphate concrete prepared by KH₂PO₄ were lower than that prepared by NH₄H₂PO₄ and decreased as the ratio of P/M reduced. The surface area of phosphate cement increased from 210m²/kg to 400m²/kg, the fluidity and strength firstly increased, and then decreased. The fluidity and strength of phosphate prepared by medium sands were lower than that prepared by fine sands or super-fine sands. Fast harden and early strength phosphate concrete of high fluidity can be prepared by three kinds of coarse aggregate, namely 5～10mm, 5～20mm and 5～25mm. Besides the ratio of cement and aggregate had a significant effect on the fluidity and strength, and the best ratio fell between 1:1 and 1:2.

Abstract: The Magnesium phosphate cement was prepared from MgO and NH₄H₂PO₄. The changes of the strength, appearance and hydration products of the magnesium phosphate cement were investigated, which are soaked in sulfuric acid solution, sodium hydroxide solution, sodium sulfate solution and magnesium sulfate solution. Besides, the impermeability and salt frost resistance of magnesium phosphate cement were analyzed. The results show that magnesium phosphate cement has good resistance to sulfate erosion, especially the anti-corrosion ability of magnesium sulfate. However the alkali resistance of the magnesium phosphate cement is poor. Therefore, the magnesium phosphate cements are not appropriate to be used in alkaline environment as cementitious material. The resistance of the magnesium phosphate cement to chemical attack is closely related to the stability of the hydration product MgNH₄PO₄• 6H₂O. The magnesium phosphate cements have good impermeability and salt freezing resistance.

Abstract: The relationships between the mechanical properties of modified concrete and the composition of latex blend were studied. Influence of steel fiber and polypropylene fiber on performance of modified concrete was analyzed on that basis. The results indicate that the contradiction between the strength and the damping property of normal concrete will be relieved to some degree by controlling the proportion of latex blend. The adding of fiber can modify the damping property of concrete, while it has a little effects on the compressive strength and elastic modulus of concrete.

Abstract: Interaction between cement and a kind of sulfate compatible polycarboxylate type admixture (PCA) and action mechanism of the novel water reducer were investigated. Experimental results indicate that adsorption amount of PCA on surfaces of cement particles is lower than that of polynaphthalene sulfonate condensate water reducer (PNS) because of the formation of more ettringite and calcium monosulfoaluminate, and calcium monocarboaluminate when CaCO3 presents in hydration system, even at initial period of hydration. Results from XRD analysis, derivative thermogravimetric (DTG) analysis and chemical analysis all verify the benificial effect of sulfate compatible PCA on initial and early age hydration of C3A. An establishment of electrostatic repulsion by grafting SO3- in molecule structure of PCA may result in a more negative zeta potential in the dispersion system. The improved dispersibility and fluidity retention are the result of a combination action mechanism of electrostatic repulsion cooperating with steric hindrance, and the acceleration effect of sulfate compatible PCA on initial and early age formation of ettringite and AFm phase. A combined high range water reducer mainly consisting of sulfate compatible PCA and PNS was made up based on the experimental and theoretical investigation results.

Abstract: This paper investigates the effect of fly ash content on unconfined compressive strength, cleavage strength and resilient modulus of cement-fly ash stabilized crushed stones. The relationships between mechanical parameters were also studied. The results show that with fly ash content increasing, the unconfined compressive strength and cleavage strength were increasing firstly but decreased then, and the resilient modulus were decreasing. The brittleness index was increased by the increment of fly ash content. It can be concluded that the optimal fly ash content in cement-fly ash stabilized crushed stones is between 10% and 15%, and increment of fly ash content can improve its crack-resistance.

Abstract: The impermeability and other performance of sulphoaluminate cement were studied, which mixed with redispersible polymer powders. With the help of SEM and mercury intrusion apparatus, the morphology of the hydrates and the pore structure of the cement mortars were observed. The impermeability mechanism of redispersible polymer powders in sulphoaluminate cement mortar was analyzed. The results show that sulphoaluminate cement mortar could be modified by adding redispersible polymer powders. The flexural strength of sulphoaluminate cement mortar could be increased by adding redispersible polymer powders, and compressive strength of sulphoaluminate cement mortar could also be increased to a certain extent. When the mass fraction of redispersible polymer powders was 0.9%, the flexural strength and compressive strength reached 9.2 MPa and 52.5 MPa. When small amount of redispersible polymer powders was added, the impermeability of modified sulphoaluminate cement mortar was improved significantly. When the mass fraction of redispersible polymer powders exceeded 0.9%, impermeability of Sulphoaluminate cement mortar would not be improved significantly. Due to redispersible powders gap filling and film forming, the interface of cement and aggregate is more closed, total porosity decreased and unharmful porosity increased when redispersible polymer powders is added.

Abstract: This paper measure moisture porosity to test pieces of explosive lining. So are the test pieces curing in standard condition and curing in equal condition. The measured moisture porosity data of the three kinds of test pieces after flooding is analyzed. The results indicate that the moisture porosity of explosive lining test pieces is higher than that of curing in standard condition and curing in equal condition. And the different value of moisture porosity increase as the standing time moves on. There is no significant difference in water-loss porosity among the explosive lining test pieces and curing in standard condition ones and curing in equal condition ones.

Abstract: Mechanical properties of pavement concrete with nano-particles are experimentally studied and compared with that of plain pavement concrete. The test results indicate that the flexural, compressive and splitting tensile strengths of pavement concrete with nano-particles are all improved with different extent. Firstly, the mechanical properties of pavement concrete are enhanced with the increasing content of nano-particles, and the peak values are achieved at certain content. Subsequently, the mechanical properties of pavement concrete are reduced with the increasing content of nano-particles. The optimum amount of nano-TiO₂ and nano-SiO₂ added into pavement concrete are respectively 1.0% and 2.0%. There is a significant linear relationship between flexural and compressive strengths of pavement concrete with nano-particles.

Abstract: A parameter of crack resistance Φ is proposed as an index to assess crack resistance of RCC comprehensively. The higher the value of Φis, the better crack resistance of RCC becomes, and it was tested and verified by indoor experiment. Meanwhile, time effect of the parameter is also studied deeply, and the characteristic of development of crack resistance is presented. Ф changes with the passage of the time. Its value decreases before 14 days, but increases after 14 days, and it is minimal at the age of 14 days, which means that crack probably exists. Finally, We improve crack resistance of RCC by improving transition zone and toughness of binding materials, optimizing aggregate and adding admixtures etc.

Abstract: Kaolin is a material with broad sources and a low price. Metakaolin is made from kaolin which is calcined, finely ground at an optimum temperature of 750 being kept constant for 4 hours. High strength and performance concrete can be mixed from metakaolin as a substitute for equal mass cement. The influences of 5%, 10% and 15% metakaolin in substitution of equal cement masses were studied on the mechanical properties of high-performance concrete. The test results showed that the addition of metakaolin improved the cubic compressive strength, splitting tensile strength and flexural strength of HPC, among which the improvement in compressive strength was the most siginificant, and simultaneously, there was also an improvement in concrete toughness in a certain degree. The optimum content of metakaolin is 10% resulting in an increase of the cubic compressive strength of concrete by 8.3% correspondingly.