International Concrete Abstracts Portal

The two most essential properties of self-compacting concrete (SCC) are high flowability and high segregation resistance. To combine these apparently incompatible properties, it is necessary to have complete control over the rheology of the concrete. This can be achieved by limiting the volume of the coarse aggregate in combination with a high powder content. This contribution mainly focusses on the influence of the nature and the grading curve of the powder on the rheological properties of SCC. In the experimental program two limestone powders are studied in different combinations with a portland cement. The effect on the rheology of the SCC is investigated by means of the slump flow test and the V-funnel. Also the influence on air content and compressive strength is studied.

This paper compares the structural performance of full-scale (300 x 300 x 3000 mm) columns cast using ordinary concrete and self-compacting (SCC) concretes with stirrup configurations representing different degrees of confinement. SCC and ordinary concretes having compressive strengths of 35 MPa (housing) and 60 MPa (civil engineering) were used to cast a total of eight columns. Two pairs of columns were cast using ordinary concrete and SCC. For each pair of the reinforced columns, one column was tested in uniaxial compression to determine its load carrying capacity, while the other one was used to take core samples to determine the distribution of in-situ compressive strengths along its height. The core results were compared to strengths determined on control cubes cured in standard conditions (water) and in air. In general, the in-situ compressive strengths of SCC were closer to standard cube strength than those of ordinary concrete. The distribution of in-situ properties was found to be more uniform in the case of SCC than that of the ordinary concrete. The compressive strength and the ductility of SCC and the ordinary concrete obtained from the 3-m column tests are also compared in this paper.

The Reactive Powder Concretes (RPC) are well known for their high strength, but they also present good performances regarding durability aspect due to their very dense microstructure. Studies were made to evaluate the durability of RPC to : freeze-thaw scaling, carbonation, chloride ions diffusion, abrasion coefficient and shrinkage. Their very good performance characteristics have led to a specific research programme to evaluate the long-term durability of RPC for nuclear waste containment. Several kinds of potential degradation are studied, but here only the attack by de-ionised water, a very severe leaching test, will be presented. After pre-determined periods, the material was analysed regarding its microstructure (altered depth, composition and mineralogical changes), porosity and ion transport properties. The results of SEM, X-Ray diffraction, mercury intrusion porosimetry, BET pore-size and tritium diffusion coefficient analyses are presented.

We have studied the effects of autoclaving under saturated vapour at 18OOC on the physical and mechanical properties of reactive-powder mor-tars reinforced with brass coated steel fibres. The system consisted of portland cement (ASTM Type V), silica fume, natural silica sand (maximum grain size <1 mm) an acrylic super-plasticizer, and brass coated steel fibres (L= 13mm, 0= O.l8nm); a water-to-cement of 0.255 was used to obtain a flowable sys-tem. Specimens were subjected to high pressure steam curing for 3 hours after preliminary curing at normal temperatures and for different times. Samples pre-cured at normal temperature for 24 hours and 3 days were autoclaved for up to 12 hours. Autoclaving generally produced beneficial effects on the mechanical properties both in terms of flexural and compression strength. High pressure steam curing for 3 hours of specimens pre-cured at ambient temperature for 3 days yielded flexural strength of 30 MPa and compression strength of 200 MPa. The strengthening mechanisms depend only in part on the greater degree of hydration as the hydrated phases that form in the systems prepared with low w/c are highly impermeable. The main effect appears to be the result of modifications to the microstructure that manifests itself as a reduction in porosity and hence in better mechanical properties.

This paper deals with trial testing on concrete reinforced by different combinations of carbon-steel, polypropylene-steel or steel-steel hybrid fibres in the low volume content range to ensure high electrical resistivity of the fibre concrete. Optimum reinforcement composition is obtained for (compression, splitting tension, and flexural) strength testing conditions and for post-peak behaviour. The effect of various measures adopted to promote uniform fibre distribution are assessed by impedance measurements. During the testing program, fibre distribution is checked by microscopy and SEM.