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.

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, the effects of the volume fraction of steel fiber. amount of silica fume, and their composite on fatigue perfomance and the mechanism of fatigue damage are investigated. The fatigue equations of steel fiber reinforced concrete and reinforced high-strength concrete are presented. Test results shaw that the effect of volume fraction and length diameter ratio on fatigue performance of concrete is extremely prominent. When silica fume, steel fiber, and their composite are added to high-strength concrete, since the effecss of the two of the nucleation and pozzolanic reaction of silica fume are in the cement marrix, and the effects of steel fiber on the strengthening toughening, and crack arresting in the composite, the interfacial structure of both the fiber cement matrix and aggregate cement matrix is strengthened. The soace superimposing of the effects of the two of the fiber-cement matrix and aggregate-cement matrix appear in the fiber reinforced composite. The double effect af interfacial strengthening and space superimposing of the fiber-cement matrix and aggregate-cement matrix is prodaeed and the inrerfacial structure and character are improved, the process of strengthening. vanishing, and restrengthening of the interface Is caused, and she dimension and the amount of crack sources are reduced. thus delaying crack extension and propagation and the protess of fatigue damage. evidently protonging fatigue life.

In this paper, the flexural, split tensile, impact and fatigue performance of steel tiber reinforced silica fume high-strength concrete (SIFUMHSC) under static and dynamic loads are studied. The effect of the amount of silica fume on its performance, the strengthening effects of siilca fume partieIe and steel fiber and their composite effect are discussed. Test results indicate to a full extent that different amounts of silica fume substituting for cement can remarkably improve the static and dynamic mechanicaI behaviour of steel fiberr einforced SIFUMHSC with other conditions unchanged and that the main realon for the change is that the addition of silica fume brings about a double interracial strengthening effect of fiber. cement matrix and aggregate-cement matrix, thus improving the structure and characteristics of the interface. When the addition of silica fume is adequate, the Hv-d, Ia-d and CHAS-d urves tend to be horizontal, wish dlfferences disappearing between the interiacla| foyer and matrix, so that the size and number of crack sources in the interracial zones and the whole matrix become smaller and less, and strengthening effects are better developed. This is the key to the desired performance of steel fiber reinforced SIFUMHSC.

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.