The mechanical properties and pore structure of fiber reinforced high strength concrete subjected to different high temperatures and cooling regimes were investigated. The results showed that the residual strength of high strength concrete with or without fibers worsened after exposure to high temperatures. Evident drop in compressive and splitting tensile strengths took place between 400°C and 600°C. However, the decline in flexural strength mainly took place before 400°C. Among the specimens, the concrete with 10% of silica fume, 25% of fly ash and 1% of steel fiber provided the highest residual strength and relative residual strength. Steel fibers played a significant role in preventing the worsening of the mechanical properties, particularly at the temperature from 400°C to 600°C. Thermal stress was not the key factor that caused the spalling or explosive spalling in high strength concrete under high temperatures. The re-curing brought recovery of the residual strength in the concretes damaged at high temperatures due to the remarkable improvement of the pore structure.

Fiber-reinforced cement for piezoelectricity and pyroelectricity is introduced, as these phenomena are useful for the sensing of strain and temperature. The use of short steel fibers (8 µm diameter), together with polyvinyl alcohol, as admixtures greatly enhances these effects, thereby attaining longitudinal piezoelectric coupling coefficient 3 x 10-" mN (10kHz), and pyroelectric coefficient 6 x 10$ C/mz.K (10 kHz). The piezoelectric effect is comparable in magnitude to that of PZT. However, due to the high value (2,500) of the relative dielectric constant, the piezoelectric voltage coefficient and pyroelectric voltage are comparable to or even lower than those of plain cement paste or carbon fiber (15 µm diameter) cement paste. Carbon fiber cement paste and plain cement paste are comparable in the piezoelectric coupling coefficient, piezoelectric voltage coefficient and pyroelectric voltage, though the pyroelectric coefficient is higher for carbon fiber cement paste than plain cement paste.

This paper reports on a series of dynamic splitting tensile tests on 70 mm diameter cored concrete and steel fiber reinforced concrete (SFRC) specimens at moderate strain rates. A modified split Hopkinson pressure bar (SHPB) was specifically developed to test such large diameter heterogeneous specimens. Details of the modified SHPB and a novel striker bar are presented. Dynamic strength magnification of up to 4.5 times the static strength at moderate strain rate was obtained. For the SFRC specimens, hooked-end steel fibers were used with 0.3% fiber volume concentration. A high-speed camera with framing rate up to 106 frames per second was used to record the crack propagation mechanism and the progressive fracture of the specimens in tests. Numerical simulation of the test is briefly presented and discussed. Good approximation of the response is obtained.

Damage due to recent earthquakes and the high costs of repairing old and building new structures emphasizes the need for novel ways of designing cost-effective and more seismically resistant buildings. To address this problem, the structural system considered in this paper is constructed with composite materials that display excellent earthquake-resistant properties such as high strength, high ductility and increased energy dissipation capacity. The particular composite used in this project is High StrengthLightweight Aggregate Fiber Reinforced Concrete (HS-LWA FRC). Its use in concretefilled steel tubular (CFT) columns allows for both: (a) improved seismic resistance and (b) possibly a faster and more cost-effective method of construction, than is the case with conventional buildings. The main goal of this research was to manufacture and study the seismic performance of such a composite CFT column. The ductility, stiffness degradation, energy dissipation and hysteretic response of the CFT member are reported. Testing of the CFT revealed that adequate strength was developed in the critical section, with respect to the predetermined yielding of the system. The use of fibers prevented an otherwise extremely brittle failure of HS-LWA concrete and increased its capacity for lateral expansion, leading to a ductile response of the critical column zones. As a result, large levels of ductility and energy dissipation capacity were measured during testing.

During the last 4 years a large testing program has been carried out in order to investigate the shear capacity of concrete beams containing longitudinal reinforcement and steel fibers. The results of this research program are presented here and compared with calculated values. For the calculations two models were used: the model proposed by RILEM TC 162-TDF and the model of Imam which is originally derived from a formula proposed by Bazant and Sun. The results of this comparison indicate that the RILEM method is a conservative approach. Especially the contribution of the stirrups and the influence of the shear span to depth ratio are underestimated. In the formula of Imam the contribution of the stirrups is calculated in the same way as in the RILEM method and consequently underestimated. However, for SFRC beams containing longitudinal reinforcement but without stirrups the correlation between experimental results and values calculated with the formula of Imam is fairly good.