Advanced Cement Based Materials最新文献

Accelerated strength testing using the boiling water procedure of ASTM C 684 was performed to evaluate this test method for use in the routine quality control of concrete made of local materials with particular emphasis on the use of blended cements, and in the prediction of potential quality and strength of concrete at later ages. Large number of groups of standard concrete specimens are sampled; in each group one cube represented the accelerated strength and is tested at 28.5 h while the other one is normally cured and tested at 28 days. Test results were recorded and statistically evaluated. A computer program was developed to carry out the numerical statistical computations and regression analysis. Correlation between the 28-day compressive strength and the corresponding accelerated strength was established considering the utilization of local materials and practices. The outcome of this study in the form of prediction models confirm that accelerated strength testing could be accepted in lieu of the standard 28-day testing. The conclusions derived may provide experimental evidence in favor of implementing the standard boiling water method for use in relation to quality control and prediction of concrete strength at later ages. Advanced Cement Based Materials 1997, 5, 49–56.

In this study, the rebar-concrete interface properties were investigated by conducting the single rebar pullout test. Using a combination of the stress approach and fracture mechanical theory, the corresponding material parameters were obtained and the model was verified as being suitable for reinforced concrete composite material. Advanced Cement Based Materials 1997, 5, 57–65.

Dielectric amplification (dielectric constants >80) is observed in cement pastes at early ages. Standard nonlinear least squares fitting routines yield artificially large “capacitances” when constant phase elements are employed. Instead, capacitance vs. frequency analysis provides reliable evidence of dielectric amplification. A physical model system consisting of a polycarbonate box with electrodes at each end, divided into two compartments by a polycarbonate barrier with a single hole, and filled with electrolyte solution, simulates the impedance response in young cement pastes. The barrier represents hydration products whereas the hole represents the constriction between two adjacent capillary pores, i.e., the pore network remains percolated. Dielectric amplification is inversely proportional to barrier thickness, i.e., it decreases as the barrier (product phase) thickens. Impedance spectra from real pastes vs. water/cement (w/c) ratio and during freezing or solvent exchange (to preferentially reduce the conductivity of the capillary pores) exhibit significant dielectric amplification, even after freezing or exchange, suggesting that C-S-H gel also has a dielectrically amplified microstructure. Advanced Cement Based Materials 1997, 5, 41–48.

This review deals with the recent progress of developments in concrete-polymer composites, which are classified into three types: polymer-modified (or cement) mortar (PMM) and concrete (PMC),polymer mortar (PM) and concrete (PC), and polymer-impregnated mortar (PIM) and concrete (PIC). A great interest in the concretpolymer composites is currently focused on high-grade redispersible polymer powders, repair and durability-improving materials for re-inforced concrete structures, mass production systems, automated cast-in-place application systems, artificial marble products, machine tool structures, and field polymer impregnation systems. Environment-conscious developments are also conducted in the concrete-polymer composites.

A fundamental theory in colloid science is the DLVO theory (named after the four contributors: Derjaguin, Landau, Verwey, and Overbeek). This theory and relevant basic concepts are reviewed and applied to cement systems to determine the state of flocculation for cement pastes. Both theoretical and experimental evidence suggest that normal, neat cement suspensions are either flocculated or coagulated. Because of the high ionic strength in the aqueous phase, the degree of flocculation or coagulation is not sensitive to the variation of the zeta potential, for zeta potentials between −20 mV and 20 mV.

An experimental program confirms that the peek-load method can be successfully applied to splitting tension tests to determine fracture parameters K_Ic^S and CTOD_c of the two-parameter fracture model from the measured peak loads. The peak-load method requires distinct specimens. It is found that a hole drilled at the axis of splitting tension cylinder can largely expand the specimen distinction. Combination of tests on splitting tension cylinders with and without a hole raises the reliability of the K_Ic^S and CTOD_c values determined by the peak-load method.

This paper investigates the effectiveness of transition zone densification on the fiber-cement paste system. By controlling the water: cement (w:c) ratio and the condensed silica fume content, environmental scanning electron microscopy studies confirm that transition zone densification can be achieved in all brass, steel, and polyethylene fiber-cement systems. However, single fiber pullout tests indicate that densification only enhances the brass-cement paste interface bond strength and not the other systems. Further microscopy investigation of the surface of fibers peeled off from a composite fracture surface and of the groove left by the fiber on the cement paste suggests that bond failure for the brass-cement system is of a cohesive type, whereas bond failure for the other two systems is of an adhesive type. It is concluded that the transition zone densification technique should be effective in fiber-cement systems in which bond strength is controlled by cohesive failure of the transition zone material.