In this paper, the electrochemical impedance spectroscopy method is applied to characteristic the hydration procedure in cement materials. And a new equivalent circuit model is developed to express the hydration procedure of cement material. As cement paste is a complicated electrochemical system with multi-phase transmission, the equivalent circuit model is considered with the additional double layer capacitance effect at the interface among the hydration products in cement materials. It can express the electrochemical station in cement material, as the multi-phase mass transmission in the cement-based material during the hydration procedure.

The accumulation of fly ash leads to severe problems in ecological environments. Various ways to excite the activity of fly ash in Portland cement based cementitious materials have been carried out for many years. In the present study, effect of large volume of fly ash in phosphate cement was studied. Dead burned magnesia, two phosphates (monoammonium phosphate and monosodium phosphate), and fly ash were used. The fabricated cement mortar specimens with different fly ash dosages were cured for 28 days in the lab air. Compressive strength was determined in 1d, 3d, 7d and 28d respectively. It is showed the compressive strength reduced with increase of fly ash content and increased with the curing time. After cured 28 days, the compressive strength of cement mortar developed to14MPa, when 80% fly ash was used. The reaction product, Na2HPO4•17H2O was found by X-ray diffraction analysis in sodium phosphate based cement. No ammonia gas was emitted and large volume of fly ash can be used in cement prepared from sodium phosphate. It is a new environmentally friendly cement material.

In this paper, the sulfate resistance properties of concrete under loading action are studied. The concrete specimens with different water/cement ratio are prepared and correlative corrosive experiments are carried out under single damage factor (SDF) and multiple damage factors (MDF), which is relative with drying and wetting cycles. Dynamic elastic modulus is taken to characteristic the sulfate resistance properties of concrete under the action of loading, drying and wetting cycles and sulfate corrosion. Results show the corrosion mechanisms of sulfate attack due to single damage factor and multiple damage factors were not all the same, and multiple damage factors could indicate the concrete structure due to sulfate attack more exactly.

An industrialized multi-layer precast concrete building with middle-joint beams and columns frame system has been developed by China VANKE CO., LTD. The building is the first industrialized multi-layer precast concrete building for experimental purpose in China. A middle-joint beams and columns method has been utilized with beams and columns split in the middle place. The whole frame structure is then integrated into a unity through precast beams, precast columns, and reliable cast-in-place column-column and beam-beam joints. This paper presents the key points and difficulties during the building design process, introduces the structural design of column-column and beam-beam joints, and analyses the advantages and weaknesses of middle-joint beams and columns frame system.

Magnesium phosphate cements (MPC) with larger volume of fly ash were studied in the present work. Dead burned magnesia, phosphates and fly ash were the components of MPC. The volume of fly ash in MPC was 70%, 75% and 80%, respectively. Three phosphates, monosodium phosphate (MSP), monopotassium phosphate (MPP) and monoammonium phosphate (MAP) were used. Compressive strength of the three MPC mortars with different fly ash content was determined. Results show that the compressive strength reduced with the proportion increase of fly ash, increased with the curing time. After cured 28 days in the lab air, the compressive strength of cement mortar can reach 14MPa, when the fly ash dosage was 80% by weight of cement. The reaction product is struvite of potassium (KMgPO4•6H2O) in potassium phosphate based MPC, and hydrated sodium phosphate (Na2HPO4•17H2O) in sodium phosphate based MPC. The results indicate that MPC has capacity to bond large volume of fly ash. A new way to utilize fly ash in a large scale can be realized by phosphate bonding.