This publication contains the proceedings from the Ninth CANMET/ACI International Conference on Recent Advances in Concrete Technology, held in Warsaw, Poland, in May 2007. The nine papers include optimization of mixture proportions of normal, high-performance, and self-consolidating concrete; reactive powder concrete mixtures for producing thin precast elements; and efflorescence of concrete products for interlocking block pavements. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-243

The roadside safety barrier is a protective barrier that is erected around a racetrack or in the middle of a dual-lane highway in order to reduce the severity of accidents. Recently, interest in portable roadside safety barriers has heightened the interest in the development of a low-cost and high-performance alternative to the conventional safety barrier system. A study has been undertaken to characterize fresh and hardened properties of flue gas desulfurization (FGD) cellular concrete (CC) using foaming admixture towards the development of a lightweight roadside safety barrier. Test results indicate that FGD CC using a foaming admixture can be effectively used in manufacturing lightweight roadside safety barriers.

In this project several reactive powder concretes (RPCs) were studied. In particular their mechanical performance in relation to the type of cement used, the dosage of silica fume, and the amount of steel fibers. Compressive strength, flexural strength, and tangent elastic modulus was monitored with age for RPCs prepared with a water to cement ratio of 0.25. Silica fume was added to the mixture at a dosage up to 27% by weight of cement. An acrylic-based superplasticizing admixture was used at a very high dosage of about 10% by weight of cement in order to achieve very fluid workability. Optimum mechanical performance was obtained for the mixture prepared by using steel fibers at 20% by weight of cement and by adding silica fume at 26% by weight of cement. This mixture was characterized by 28-day compressive strength of 145 MPa, flexural strength of 35 MPa, and tangent elastic modulus of about 57 GPa. On the basis of experimental results, the use of reactive powder concretes for manufacturing thin precast elements appears to be competitive with other and more traditional materials and technologies.

This article outlines an experimental and numerical study on the optimization of mixture proportions of concrete. For this purpose about 500 mixture proportions were studied in the laboratory and compared with about 500 mixture proportions from industry. Normal, high-performance and self-compacting concrete were included in the investigation. Additives such as fly ash, limestone filler, silica fume and slag and different kinds of cement were included in the program. The w/c varied between 0.15 and 1, with 28-day cylinder strength ranging from 20 to 120 MPa. The results show with high significance that ideal particle distribution curves exist for each cement and concrete type taking into account also the related water demand and the correlation between w/c and strength. The study resulted in a highly efficient commercially available computer program.

This paper presents the results of an experimental investigation to determine the validity of 0.45-power chart in obtaining the optimized aggregate gradation for improving the strength characteristics of high-performance concrete (HPC). Historically, the 0.45 power chart has been used to develop uniform gradations for asphalt mixture designs; however it has now been widely used to develop uniform gradations for portland cement concrete mixture designs. Some reports have circulated in the industry that plotting the sieve opening raised to the 0.45 power may not be universally applicable for all aggregates. In this paper the validity of 0.45 power chart has been evaluated using quartzite aggregates. Aggregates of different sizes and gradations were blended to fit exactly the gradations of curves raised to 0.35, 0.40, 0.45, 0.50 and 0.55. Five mixtures, which incorporated the aggregate gradations of the five power curves, were made and tested for compressive strength and flexural strength. A control mixture was also made whose aggregate gradations did not match the straight-line gradations of the 0.45 power curve. This was achieved by using a single size aggregate and sand. The water-cement ratio and the cement content were kept constant for all the six mixtures. The results showed that the mixture incorporating the 0.45 power chart gradations gave the highest strength when compared to other power charts and the control concrete. Thus the 0.45 power curve can be adopted with confidence to obtain the densest packing of aggregates and it may be universally applicable for all aggregates.