International Concrete Abstracts Portal

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.

Type K Shrinkage Compensating Concrete (SCC) concrete is uniquely suited for use in slabs and walls because it typically requires fewer expansion joints than a convention portland cement (PC) concrete. This allows for continuous placement of much larger slabs and walls and facilitates the construction of high performance smooth slabs with few interruptions. Typically shrinkage-compensating concrete construction practice is to pour adjoining wall sections a minimum of five days apart in order to allow for the initial expansion of the material. The need for unrestrained expansion is implied in the ACI 223R-10 Design Guide in Chapter 5 in a discussion on sequencing the placement of wall segments. This paper discusses testing that was performed at two different locations, spanning both two different times of year and two unique climates. The tests used vibrating wire strain gages (VWSG) to investigate the restrained behavior of a wall segment in a six million gallon clear well tank in Springfield, IL, as well as the unrestrained behavior of two slabs-on-grade in Los Angeles, CA. Measurements were taken for a minimum of 30 days and a maximum of 170 days. Testing results are then compared to similar scenarios using ordinary PC concrete.

In order to be cost-effective, surface repairs carried out on concrete structures have to perform satisfactorily over a sufficient period of time. Among the factors that can affect the durability of concrete repairs, drying shrinkage is certainly one of the most significant. Shrinkage compensating concretes (ShCC’s) represent a very attractive alternative to prevent shrinkage cracking in repairs. This paper summarizes the results of a project devoted to repair ShCC’s made with an expansive component, more specifically their robustness as a function of selected parameters. The investigated expansive systems were either, a calcium sulfoaluminate-based (ASTM Type K cement or Type K component) or calcium oxide-based (ASTM Type G component). The assessment of robustness addressed the influence of the mixture design parameters (cement composition, type and dosage of expansive agent, w/cm ratio) and the curing conditions (moist curing conditions, temperature) upon the ShCC’s expansive behavior, the bond between ShCC repairs and an existing concrete substrate, and the chemical prestress generated through the bond. Overall, the results yielded in this study demonstrate the remarkable potential of ShCC’s as crack-resistant and durable repair materials.

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.

In the modern transportation industry, nearly all bridge decks are constructed of concrete. Of the concrete bridge decks currently in service across the US, almost all contain large numbers of cracks. These cracks are the bane of deck longevity. They allow the ingress of salts that cause corrosion of the reinforcing steel, exacerbating concrete cracking and loss of structural capacity. A survey conducted several years ago by Folliard et al. (2004) for the FHWA found that more than 100,000 bridges suffered from early-age cracking. This paper presents a case study of bridge decks in Ohio and Michigan that are essentially crack-free. Some of these bridge decks are located on high volume highways/interstates and are up to 30 years of age. In addition, several of these bridges have adjacent standard Portland cement concrete sister bridges built at the same time, with identical spans and construction details handling traffic flowing in the opposite direction. Comparison of these bridges offers unique insight into a simple, effective solution for mitigation of bridge deck cracking.