International Concrete Abstracts Portal

Self-compacting concrete, recycled concrete as aggregate, calcium nitrate accelerators—these are just a few of the topics covered in the 47 papers included in ACI SP-200, Fifth CANMET/ACI International Conference on Recent Advances in Concrete Technology. You’ll be able to compare the structural performance of full-scale columns using ordinary and self-compacting concretes and with stirrup configurations representing differing degrees of confinement. You’ll also learn about a procedure that improves the quality of concrete made using aggregate produced from recycled concrete, and about experiments showing that, at 5 °C, calcium nitrate is a much more effective accelerator than calcium chloride. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP200

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 presents the test results on the study of reinforced concrete (R/C) columns strengthened with carbon fiber sheets (CFS). The purpose of this research was the evaluation of the CFS confinement characteristics of square reinforced concrete columns. The test specimens consisted of seventeen square columns (200x 200mm cross-section and 400mm height). The test columns were fabricated with different lateral reinforcement ratios. The tests were performed with different CFS reinforcement ratios and reinforcing methods to investigate the effects on the strength and deformation characteristics of concrete columns. Test results were characterized according to failure patterns, maximum loads, and strain distribution along the column longitudinal axes.

Lightweight concrete with lower water absorption for thin structural elements was goal of investigation. Polypropylene fibers contributed to concrete ductility. For lower bulk density we used polystyrene grains. We used polymer modified concrete for realization of better adhezion between concrete and fiber. Polymer membranes cover the. micro - fissures wich may appear due to shrinkage, so polymer modified concrete has smaller water absorption. The influence of polypropylene fiber and cement quantity on properties concrete is investigated in this paper. Experimental work included several kinds of concrete, made with different cement contents, consistency, quantity of polypropylene fibers and with polymer latex, styrenebutadiene rubber modifier. River aggregate with grain size of up to 8 mm was used. The polymer portland cement concrete properties depend, not only on composition but also on the way of preparation, compacting and curing. Curing includes: 1 day in wet conditions, 6 days in the water followed by 21 days in the air. Compressive and splitting tensile strength and water absorption values are reported. It can be concluded that using of polypropylene fibers have better effect on splitting to compressive strength ratio for concrete with bulk density lower than 1800 kg/m3.

Quality of concrete with recycled aggregate is generally lower than that of virgin aggregate. The main reason is that, recycled aggregate with its higher water absorption property has porous mortar matrix around than that the virgin aggregate and hence develops an inferior bond. In order to improve the quality of recycled aggregate concrete, an innovative method is proposed in this paper. High quality recycled aggregate concrete HiRAC can be obtained through a decompression and rapid release (DC-RR) procedure applied after normal mixing of concrete with recycled aggregate. Through the DC-RR procedure, the quality of transition zone between aggregate and cement matrix can be dramatically improved. In this paper, experimental studies are described on the effectiveness of DC-RR procedure on some of the mechanical and physical properties of recycled aggregate concrete. It was found that, by applying the DC-RR procedure, compressive strength of recycled aggregate concrete can be increased by about 20%, creep and carbonation depth can be reduced by about 20% and 30%, respectively.