Quantifying Stress Development and Remaining Stress Capacity in Restrained, Internally Cured Mortars

Abstract

mixture (paste, mortar, or concrete) around a steel ring. Residual tensile stress develops in the sample as it attempts to shrink but is restrained by the ring. A crack results if the stress that develops due to restraint (called "residual stress" by some) exceeds the developing tensile strength. The standard 18 suggests that the relative cracking potential of mixtures can be quantified by comparing the amount of time required to crack the samples. Shorter measured cracking times indicate a relatively higher cracking potential, whereas longer cracking times indicate a lower cracking potential. While ASTM C1581-04 18 describes a material behavior in terms of the age of cracking, the authors believe that describing the stress development, stress-to-strength ratio, or probability of cracking may be better indicators of cracking susceptibility. 19 While the standard restrained ring test is a useful standardized test, 20 it is limited in at least three ways. First, it should be operated at a constant temperature because changing the temperature of a standard ring would significantly expand or shrink the restraining ring, thereby altering the degree of restraint and stress. This effect would make it difficult to isolate and study the behavior of the concrete under the changing temperature conditions that are commonly encountered in a field structure. The second limitation is that the standard restrained ring test is a passive test. 21,22 As a result, the test waits for the shrinkage of the specimen to generate enough stress to induce cracking. This provides useful timeto-cracking comparisons between multiple mixtures and can permit stress development to be calculated, but determining the probability of cracking 16 is more difficult. 23,24 Further, the passive behavior of the test may require considerable time to induce cracking. Third, the restrained ring test can only provide restraint against samples that shrink. Samples that exhibit net expansion typically come out of contact with the restraining ring and expand freely. This limitation becomes significant when studying expansive cements, 25 shrinkagereducing admixtures, 26-28 and internal curing, 7,8,10,12,29 as these technologies often produce early-age expansion. A dual-ring testing device 30 can be used to extend the applicability of the restrained ring test. The dual-ring device, as its name implies, incorporates a second restraining ring that is located on the outer face of the sample. This additional ring provides restraint against expansion and captures the restrained behavior of expansive samples. The dual ring used in this study can also be used to study the effects of Concrete can develop tensile stress when it is restrained from shrinking freely. Standard tests, such as the restrained ring test (ASTM C1581), can be used to quantify how likely it is that a mixture will crack due to the stresses developed under constant temperature conditions. The standardized restrained ring test is a passive test where the residual stress that develops due to restraint ca...

Concrete Patching Materials and Techniques and Guidelines for Hot Weather Concreting

“…Much of this work has illustrated a need to improve the performance of HES concrete mixtures. Data has shown internal curing as a cost effective, value added methodology that reduces cracking and improves the durability and service life of concrete mixtures (Barrett, 2015;Bentz & Snyder, 1999;Bentz & Weiss, 2011;De la Varga et al, 2014;Miller, Barrett, Zander, & Weiss, 2014;Schlitter, 2010;Schlitter, Senter, Bentz, Nantung, & Weiss, 2010).…”

Documentation of the INDOT Experience and Construction of the Bridge Decks Containing Internal Curing in 2013

“…To overcome some of the drawbacks associated with this test, a new test has been developed which utilizes two concentric rings of invar housed in a semi-adiabatic chamber with a temperature regulation coil (Schlitter, Senter, Bentz, Nantung, & Weiss, 2010). This test has been utilized to show that nearly all of the autogenous shrinkage can be successfully mitigated through internal curing and greatly reduce the early age cracking potential (Schlitter, Bentz, & Weiss, 2013). The dual ring test has also been used to show the benefits of using internal curing with high-volume fly ash systems to reduce the potential for autogenous and thermal shrinkage cracking (Barrett, De La Varga, Schlitter, & Weiss, 2011;Barrett, De La Varga, & Weiss, 2012).…”

“…This reduction in thermally induced stress is largely a consequence of a lower coefficient of thermal expansion (COTE) in internally cured concretes (Wyrzykowski & Lura, 2013). An additional effect of the presence of LWA can be seen in the slope of the induced thermal stress, where the rate of stress development in the IC HPC 1 mixture is lower due to the more compliant nature of the IC HPC 1 mixture (Barrett et al, 2011;Raoufi, Schlitter, Bentz, & Weiss, 2011;Schlitter et al, 2013).…”