International Concrete Abstracts Portal

Samples of Type K shrinkage-compensating cement from all 17 mills producing that cement in 1974 were obtained and evaluated for compliance with the specification that was proposed at that time for these types of cements. The cements were also evaluated for specific gravity, fineness, heat of hydration, and expansion and drying shrinkage in mortars. An X-ray diffraction analysis was also made for each cement in an attempt to compare cements to note significant differences in composition or relative amounts of constituents. A standard concrete mixture was also made with all the cements and evaluated for air content, slump, compressive strength, expansion, and drying shrinkage. The results from these evaluations are revisited. The application of the 1974 proposed specification called attention to several short-comings in that specification.

This short work details the history of Type K shrinkage compensating cement.

This paper reexamines the authors’ experimental results on the dimensional stability of concrete slab-on-ground under a variety of environmental conditions. The experiments considered the dimensional properties of concrete slab materials using both Demec targets and vibrating wire strain gages. Realistic slab-on-ground sections were investigated in this study in that the concrete slabs were exposed to a controlled environment on the top surface and to actual ground moisture on the bottom surface. The concrete materials tested were normal Portland cement concrete (PCC), high strength concrete (HSC), concrete with shrinkage reducing admixtures (SRA), and concrete with calcium sulfoaluminate cement (CSA). The compiled database contains: 1) standard concrete material test results; 2) joint movements in concrete slab-on-ground; and 3) internal relative humidity and temperature through the slab-on-ground depth. The experimental results revealed that CSA was quite stable with little long-term shrinkage/cracking or warping, whereas PCC and HSC had continuing crack growth during 600 days of curing. The SRA exhibited a modest reduction in shrinkage/crack at the early stage, and while this decrease extended for the length of the testing no further decrease in the shrinkage growth or sectional stability was noted when compared to PCC at the end of 2 years. Evaluation of the vibrating wire strain gage method of measuring long term concrete shrinkage was found to be less prone to user bias and more accurate than the Demec target method or the ASTM C157 method.

Shrinkage compensating concrete is one of the most common products currently used to mitigate the influence of drying shrinkage cracking in slabs, beams and other structural components. Type K expansive concretes have proved effective for prevention of structural and aesthetic damage due to tensile cracking in many modern applications. However, the ACI 223R-10 technical guide still indicates that a shrinkage compensating slab cannot expand adequately if it is surrounded on all sides by mature reinforced concrete. The objective of this project was to investigate whether the presence of a stiff external restraint condition, which may be provided by adjoining concrete, prevents a Type K expansive concrete slab from compensating for shrinkage. To investigate this behavior, the field condition of a slab-to-slab interaction was simulated using a steel restraint system with varying degrees of stiffness and amounts of Type K expansive cement component. Test frames were instrumented to evaluate the force and displacement responses of the Type K expansive concrete to the different boundary conditions provided by varying the steel restraint system. The results of this investigation support a conclusion contrary to that currently found in the ACI 223R-10 guiding document. This study concludes that a Type K expansive cement concrete does not suffer a severe reduction in shrinkage compensation in the presence of a very stiff boundary condition.

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.