International Concrete Abstracts Portal

With adoption of winter maintenance strategies that typically include incorporation of aggressive deicer chemicals, pavement surfaces in cold regions are exposed to the risk of scaling damage. Reduced ride quality due to surface deterioration can eventually lead into a variety of maintenance and repair programs. Such pavement preservation programs impose significant charges to the owner agencies, while raising concerns regarding the safety issues associated with work zone areas. The present study addresses the correlation between surface hardness and concrete hardened properties. Moreover, factors that influence the concrete performance with respect to surface-abrasion resistance (hardness) were investigated. Of special interest was the relationship between surface hardness and concrete salt-scaling performance. An extensive investigation was carried out to assess the effects of various mixture proportions, curing regimes, and finishing times on surface hardness of the concrete specimens. In addition, compressive strength, depth-sensing indentation (DSI), and salt scaling tests were used to evaluate the correlation between concrete surface hardness and performance. A scaling quality classification table using abrasion mass loss values was developed. The results reflect further understanding of the relationship between abrasion resistance and salt scaling resistance that can cause defects when more than two cycles of abrasion testing are applied.

While high-volume fly ash (HVFA) concrete mixtures are attractive from a sustainability viewpoint, they are sometimes plagued by long delays in finishing, producing a performance that is unacceptable to contractors. In this paper, isothermal calorimetry studies are conducted to examine excessive retardation in HVFA mixtures based on both Class C and Class F fly ash. In addition to quantifying the retardation, the calorimetric curves are also used to evaluate the performance of mitigation strategies based on various powder additions. Powder additions examined in the present study include an aluminum trihydroxide, calcium hydroxide, cement kiln dust, condensed silica fume, limestone, and a rapid-set cement. The addition of either 5% calcium hydroxide or 10% of the rapid-set cement by mass of total solids (powders) is observed to provide a significant reduction in the retardation measured in mixtures based on either class of fly ash for the material combinations examined in this study. Thus, these two powder additions may provide viable solutions to mitigating excessive retardation, extending the use of HVFA mixtures in practice.

The use of self-consolidating concrete (SCC) can enable the reduction of labor demand for vibration and surface finishing, accelerate placement rate of concrete, and secure superior surface quality. Despite the low yield value required for deformability, SCC is characterized by a moderate viscosity to enhance cohesiveness and stability of the fresh concrete. The air entrainment of SCC for frost durability can reduce viscosity leading to greater risk of segregation and blockage of concrete flow upon spreading between closely spaced obstacles. This paper investigates the mixture proportioning of air-entrained SCC suitable for filling congested sections, such as in the case of repair of the underside of bridge deck girders, and conventional non-restricted elements. The results of a laboratory study undertaken to optimize and evaluate properties of air-entrained SCC are presented in this paper. The mixtures were proportioned with 370, 450, and 550 kg/m 3 of cementitious materials and water-cementitious material ratios (w/cm) of 0.45 to 0.50. Ternary binders containing 20% Class C fly ash or 40% ground blast-furnace slag with 3% silica fume were used. The mixtures were evaluated for slump flow consistency, restricted deformability and surface settlement, strength development, elastic modulus, temperature rise, shrinkage, perme-ability, and frost durability. Examples of the use of such concrete for repair of a densely reinforced beam in a parking structure and a moderately reinforced beam-wall element with restricted access in a powerhouse are also discussed. Test results clearly indicate the feasibility of proportioning air-entrained SCC of high stability and resistance to blockage. Optimized mixtures exhibited adequate engineering properties and durability. The field studies demonstrated the effectiveness of such high-performance concrete to repair damaged sections presenting difficulties for placement and consolidation.

Quality of concrete slab or floor is highly dependent on achieving a hard and durable surface that is plane and free of cracks. The properties of the surface are determined by the quality of the concreting operations. Furthermore, timing of these concreting operations and finishing techniques is critical. Otherwise, undesirable changes occur at the wearing surface; these may lead to soft or dusting surfaces, permeable concrete, cracking, and poor durability. This guide tells how to produce good quality floors and slabs for various classes of service, emphasizing such aspects of construction as site preparation, concreting materials, concrete mixture proportions, concreting, workmanship, and curing. Adequate supervision and inspection are required of all job operations particularly including finishing.

Many building codes require minimum sound transmission loss values, expressed as sound transmission class (STC), OF 45 TO 50. Tests of sound transmission loss were made on 8 in. (203 mm) thick concrete masonry walls and on 6 and 8 in. (152 and 203 mm) thick cast concrete walls. These walls were finished with materials intended to increase their sound transission loss. Using furring, acoustic insulation, and wallboard attachments, STC values up to 59 and 63 were obtained for the masonry and cast concrete walls, respectively. Selected STC values, reported by other investigators, for a variety of walls are included for reference.