S. J. Barnett

Fast Track Construction with High-Strength Concrete Mixes Containing Ground Granulated Blast Furnace Slag

The early age strength development of concretes containing ground granulated blast furnance slag (GGBS) at cement replacement levels of 20, 35, 50 and 70% have been investigated to give guidance for their use in fast track construction. 28-day target mean strengths for all concretes was 100 MPa. Although supplementary cementitious materials like ggbs are economical, their use has not gained popularity in fast track construction because of their slower strength development at early ages and at standard cube curing temperatures. There are however indications that supplementary cementitious materials are heavily penalized by the standard cube curing regimes. Measurements of temperature rise under adiabatic conditions have shown that high levels of cement replacement by ggbs, e.g. 70% are required to obtain a significant reduction in the peak temperature rise. However, despite that these temperature rises are lower than those of portland cement mixtures they are still sufficient to provide the activation energy needed for the reaction of ggbs to “kick-in” earlier. The early-age strength of companion cubes cured at 20 degrees. The high early age temperatures are shown to be especially beneficial to ggbs concretes. Maturity measurements will be needed in order to take advantage of the enhanced in-situ early age strength development of ggbs concretes. The contractor needs to be able to confirm that the actual strength of the concrete in the structure at the rime of formwork removal exceeds a certain compressive strength. Maturity functions like the Nurse-Saul and the Arrhenius equation have been examined for their applicability to ggbs concretes. Activation energies, required as input for the Arrhenius equation, have been determined according to ASTM C1074-98.

Study of fibre distribution and orientations in UHPFRC by electrical resistivity and mechanical tests

ABSTRACT This paper presents experimental tests carried out on steel fibre reinforced concrete samples, including mechanical tests as well as non-destructive technique (electrical resistivity) and non destructive technique on cores (X-ray). Electrical resistivity measurements are done as a blind test, to characterise the electrical anisotropy and deduce the distribution and the orientation of fibres. These results are compared to X-ray imaging to check the quality of the non destructive evaluation. Then, flexural and compressive strength are measured on specimens to assess the influence of fibre distribution on the concrete properties.

Modelling the response of UHPFRC panels to explosive loading

Explosive testing of full-size fibre-reinforced concrete panels was conducted at GL Industrial Services at Spadeadam test site, Cumbria, England in 2008. The panels were manufactured by VSL Australia and shipped to Spadeadam for testing. This paper reports these tests and a simplified analysis of the response of the panels. Each panel measured 3.5m by 1.3m by 100mm thick. The panels were contained within a large concrete enclosure to minimise clearing around the sides from the blast wave and placed between 7m and 12m from a 100 kg TNT equivalent explosive charge. Two of the panels were fabricated with different levels of steel fibre dosage. The remaining two panels were fabricated with steel fibres together with supplementary steel bar reinforcement. Numerical computer modelling was carried out using the Autodyn package to predict the behaviour of the four panels before testing. Based on the predictive modelling, each panel was placed a suitable distance from the explosive charge so as to cause permanent damage but not total structural collapse. The maximum flexural tensile strain rate evaluated on the back face of the panel was in the region of 1.0s -1 . Simplified modelling of the panels was also carried out using a singledegree-of-freedom representation together with a resistance-deflection relationship that took account of characteristic brittle cracking and ductile softening behaviour following ultimate capacity. An outline of the method with results is given in the paper.