International Concrete Abstracts Portal

This paper presents the evaluation of a new high tenacity monofilament polypropylene fiber for reduction of plastic shrinkage cracks in concrete. The crack reduction potential of the fiber was studied using cement-rich concrete and the performance of the fiber was compared with that of three other presently available fibers (Fiber B, Fiber C, and Fiber D). Performance of these fibers was evaluated by comparing the area of plastic shrinkage cracks developed in control slabs (with no fibers) with the crack area of fiber reinforced concrete slabs. For example, the reduction of crack area due to the addition of the new high tenacity monofilament fiber was 91 percent for a dosage of 0.593 kg/m3 [1.0 lb/yd3], 86 percent for 0.297 kg/m3 [0.5 lbs/yd3] and 57 percent for 0.196 kg/m3 [0.33 lbs/yd3]. The results indicate that the new fiber with fiber length of about 18 mm [¾ inch], and a fiber dosage of 0.593 kg/m3 [1.0 lb/yd3] was most effective in reducing the plastic shrinkage cracks in concrete. For the same fiber quantity, three other fibers were less effective in reducing cracks.

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.

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.

Today, a number of engineering structures and building are being constructed to match environment and urban landscape. From an aesthetics point of view, occurrences of efflorescence on colored concrete, unfinished concrete and concrete products of these structures are critical problems. This research aimed to study and compare the efflorescence of concrete products that substituted cement with industrial by-products namely, fly ash, blast furnace slag and gypsum and normal concrete. Both concrete products and normal concrete were manufacture for paving application in form of interlocking blocks. In this paper, we use the term "non-cement" concrete to refer to the concrete not using industrial cement. A methodology is presented that enables a quantitative evaluation of the total, soluble and insoluble efflorescence and this methodology was used to analyze both non-cement concrete and normal concrete specimens. The results show that the insoluble efflorescence of non-cement concrete is less than that of normal concrete.