The addition of ufitratine powder (UFP)to concrete can improve the fluidity of concrete, showing a water-reducing effect The aim of this article was to analyze the water-reducing mechanism of UFP both experimentally and theoretically. Three UFPs-fine ground slag. highcalcium fly ash, and low-calcium fly ash--weN chosen for the study. The contrastive experiments were done to investigate the fluidity of mortars with 30%, 45%, 60%. and 75% equivalent cement replaced by fine ground slag. high-calcium fly ash. and low-calcium fly ash. respectively. The results showed the physical and chemical characteristic of the powder, such as their grain morphology, glass phase activities, densities, specific areas, and their groin eumuhdng conditions, can strongly affect their water-reducing effect.

The properties of fiber-reinfored cement-based composite materiais are dependent on the charactertstics of the fiber, the motrix, and the fiber-matrix interface. In general, the nature and behavior of the fiber and matrix are reasonably well understood, but those of the interface are known in considerably less detad. Results of an experimental program demonstrate that the addition of an acrylie polymer to fiber-reinforaed mortar and cement strengthens the matrix material and improves the structure of interface, thus increasing the interface bond strength.Tensile tests, fiber pullout tests. microhardness studies, and electron microssopy studies were conducted on mortar matrix materials. with and without the addition of the acrylic polymer. The tensile strength of the matrix material, the interfacial bond strength between the matrix and steel fibers, and the energy required for fiber debonding and pullout were incensed by a factor of almost four with the addition of 15 potent acrylic polymer by weight of cement. TO explain these incenses, the microhardness and microstructure of an annular region of the composite surrounding a fiber (interface transition ring) were investigated. Addition of the aeryhc pollymer to a cement matrix resulted in increases in micrahardness of the cement matrix material of the same order of magnitude as increases obtained in tensile strength, bond strength, and energy required for fiber debonding and pullout. Observation with a scanning electron micro-scope indicated that cracking along the fiber-matrix interface (before loading) is substantially reduced by the addition of acrylic polymer. Possible explanations for this are a reduction in the film of water that surrounds the fiber and the filling of small cracks with the acrylic polymer material itself.

A research program was carried out to investigate the residual compressive strength of high-porformance concrete (HPC) and normal strength concrete (NSC) after they were exposed to high temperatures, 8O0℃ and 1100℃, and two cooling regimes, Test results obtained showed that eompared with the strength at room temperature, the residual strength of both HPC and NSC dropped sharply after exposure to high temperatures. Water cooling, which resulted in a significant thermal shock. caused a bit more severn deterioration in strength compared to furnace cooling. Thermal shock was not necessarily the primary cause for spalling in HPC. Mereury intrusion porosimetry tests were carried out to measure variation in the pore structure of concrete. Sigaifieant changes in the cumulative pore volume curves before and after high lemperatures in both NSC and HPC were observed. The cumulative pore votume of HPC increased more remarkably than thai of NSC. The difference between the effects of the two cooling regimes on mechanical property as well as the microstmeture decreased at 1100℃ when compared 800℃.

Environmeneal scanning electron mieroscope (ESEM) was used to in sire quantitatively studu the hydration process of K-PS geopolymer cement under an 80% RH cnvironment. An energy disperion X-rap analysis (EDXA) was also employed to distinguish the chemical composition of hydration product. The ESEM micrographs showed that metakaolin particles pack loosely at 10min after mixing. resulting in the existence of many large voids. As hydration proceeds, a lot of gels were seen and gradually precipitated on the surfaces of these panicles. At teter stage, these particles were whipped by thick gel layers abd their interpaces were almost completely lifted. The corresponding EDXA resufts illustrated that the molar ratios of K/Al increase while Si/Al decrease with the development of hydration. As a result, the molar ratios of K/Al and Si/Al of hydration products at an age of 4h amounted to 0.99 and 1.49. respectivelp, which were close to the theoretical values (K/Al=1.0 Si/Al=1.0 for K-PS geopolymer cement paste). In addition, well-developcd crysthis could not been found at any ages; instead, sporgclike amorphous gels were always been observed.

In this paper, thgh-performmance concrete (HPC) ihcorporated with expansive agent and hybrid fiber, i.e., steel fiber, polyvinyl alcohol fber (PVA fiber), and polypropy[ene fiber (PP tiber), was produced. The properties measured included shrinkage and water permeation of the concrete The effect of hybrid fibers and/or expansive agent on the shrinkage and water permeation properties was investigated. Test results indicated that the hybrid fiber of different types and sizes could reduce the size and amount of crack source at different scales; hybrid fibers combthed with expansive agent provided better enhancement for shrinkage resistance and impeccability of HPC than monoincorpomnon of hybrid fibers or expansive agent; the improvemem of the shrinkage resistance and the impermeability of tbe concrete resulted from the combined use of expansive agent and hybrid flbers, which was dependent on the amount of expansive agent, types and sizes of hybrid fibers, total volume fraction of fibers, proportions of hybrid fibers, and so on. The relevant mecbanisms were also discussed based on the analysis of the test results of pore structure of the concrete.