International Concrete Abstracts Portal

The general purpose of reinforcing bars in slabs-on-ground is to control crack widths at the top surface of a slab. As the amount of reinforcement increases across the joint, the probability of out-of-joint cracking increases, as tighter cracks may occur at closer spacing than the joints. The Q&A provides some guidance on the amount of reinforcement crossing the joint and its role.

Expansive component systems provide the possibility to control the effects of concrete drying shrinkage in civil engineering applications, promoting durability for new construction and repair alternatives. Drying shrinkage is a natural consequence of concrete upon water loss after hardening. When there are restrictions such as internal reinforcement, adjacent structural elements and subgrade friction, concrete drying shrinkage can lead to cracking if no provisions are considered on the mix design or on the construction procedure. Expansive component Type G reacts chemically with Portland cement and water in the concrete mix to produce calcium hydroxide platelet crystals, which after setting, produce a volume increase. Providing internal or external restrictions, a concrete, that contains an expansive component system, can induce compression stress in the concrete mass and tension stress in the reinforcement. Concrete cracking can be reduced because such induced compression stress counteracts the tensile stress in the concrete mass caused by drying shrinkage. This article comprises a variety of applications of concrete, including the expansive component Type G, in Mexico as a solution means of improved functionality and durability of modern construction.

Owners, engineers, and contractors have been forced to contend with drying shrinkage for as long as portland cement has been used in slabs-on-ground, containment structures, and other concrete elements. The resulting cracks and warping have long-lasting impacts on both the performance of the concrete and the lifetime maintenance cost. Various construction methods have historically been used to mitigate this issue including modified mix designs, curing compounds, joint detailing, and transfer devices to reduce warping (curling). With advances in type K shrinkage compensating cement technology, however, designers and contractors now have access to a concrete that can eliminate shrinkage cracks, extend joint spacing to extremes, vastly reduce costly joint construction, and shorten construction schedules. This solution reduces not only construction costs but also maintenance costs on the structure for years to come. Shrinkage compensating concrete (SCC) produced using ASTM C845 Type K cement has been used in floors, elevated building decks, bridge decks, post-tensioned concrete, and containment structures since the mid 1960’s. Today, Type K SCC cement technology is even better understood, making way for higher performing concrete elements.

Concrete is one of the most widely used construction materials in the world. In applications where appearance, durability, and permeability are of concern, reduction of cracking is a key need. A common cause of cracking is restrained drying shrinkage. Until very recently, drying shrinkage cracking has been controlled by reducing joint spacing, increasing reinforcement, and using expansive cements and admixtures. In this paper a new shrinkage-reducing admixture (SRA) is discussed. SRAs provide a convenient means of reducing drying shrinkage as they are added during batching and mix easily into the concrete. The SRA material discussed in this paper improved workability and finishing as an added benefit. The effects of mixture proportioning, curing conditions, and SRA content on unrestrained and restrained drying shrinkage were determined. The results show that long-term drying shrinkage reductions of 50% can be achieved, and that there is a significant improvement in restrained shrinkage performance. Even though the lowest absolute values for drying shrinkage occur with proper curing, there is still a substantial reduction in drying shrinkage for specimens cured for short times. It is shown that shrinkage reduction is directly related to the SRA addition rate as a percentage of the mixing water. Furthermore, data on large-scale field experiments show that substantial reduction in cracking is obtained for concretes treated with SRA.

Examines the procedures commonly adopted for the rational design of nonprestressed reinforced concrete tanks and analyzes the accuracy and appropriateness of these procedures for achieving the goal of economical and safe structures with reasonable life spans.