A finite element model is used to examine how the properties of cementitious mortar are related to the stress development in the dual ring test. The results of this investigation are used to explain the thermal cracking behavior of mixtures containing prewetted lightweight aggregates (LWA) by quantifying the contribution of several material properties individually. In addition to the beneficial effects of using the LWA as an internal curing agent to reduce the autogenous shrinkage of concrete, the LWA also helps to reduce the potential for thermal cracking due to a lower elastic modulus and increased stress relaxation. The rate of stress development, age of cracking, and magnitude of the temperature drop necessary to induce cracking in a dual ring specimen are dependent on a variety of factors, including the coefficient of thermal expansion of both the cementitious mortar and the restraining rings, elastic modulus of the mortar, creep effect of the mortar, and rate of thermal loading. Depending on the rate of cooling, cracking may or may not occur. The slowest rate of cooling (C/h) minimizes the effects of creep while cooling rates faster than C/h can produce a thermal gradient through the mortar cross-section that needs to be considered.

these materials to be used and specified more widely in Indiana. It is recommended that a training video be developed that highlights the benefits of this material, describes its use, and discusses important features associated with placement and testing

Prepared in cooperation with the Indiana Department of Transportation and Federal Highway Administration. AbstractJoints are placed in portland cement concrete pavements (PCCP) to control random cracking. These joints provide a weakened plane that enables a crack to form in a controlled manner, relieving residual stresses that develop when thermal, hygral, or hydration movements are resisted by subgrade and adjoining pavement. While the concept of creating a weakened plane through saw-cutting is straightforward, determining the time and depth of the saw-cut has proven to be complicated. The goal of this project was to reduce the risk for joint raveling and random cracking. Specifically, this project has focused on: developing a procedure for determining the appropriate saw-cutting time window for typical pavements constructed in the state of Indiana, determining the depth of the saw-cut that minimizes the risk of micro-cracking and random crack development, and developing tools and training materials for paving contractors and state inspectors that aid in implementing the findings of this study in concrete pavements.Toward this end the project was divided into three phases. The first phase of the project consisted of shadowing five pavement projects in Indiana. From these field investigations practical information was gained which was useful in developing the laboratory testing program. The second phase of this work involved in the development of the laboratory testing program. This phase in large part was involved in the development and commissioning of a new tensile wedge testing approach to determine the early age properties of concrete. Finally, finite element simulations were performed to simulate the early-age behavior of pavements constructed under a variety of saw-cutting sequences, environmental conditions. A strength reduction factor was computed based on the depth of the saw-cut. It was shown that the time of the saw-cut introduction needs to occur before the residual stress divided by the product of the strength reduction factor and tensile strength was equal to unity. It was also shown that shallower saw-cut depths were more prone to construction and material property variability. Recommendations are made to assist contractors in determining when saw-cuts are placed that can greatly improve field operations. Joints can be induced in early age concrete using several methods which include the use of hand-tools, preformed strips, and saw-cutting. While these three approaches are all valid, practical considerations for slip-form paving operations result in the nearly exclusive use of saw-cutting as the method of choice for inducing joints. Generally it is thought that three main methods of saw-cutting joints exist including conventional wetcut (water-injection) saws, conventional dry-cut saws, and the more recently developed early-entry dry-cut saws.While the concept of creating a weakened plane by saw-cutting may appear straightforward, determining the time and depth of the saw-cut has p...

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because they can lead to raveling and spalling at the edges of the joints. Saw cuts cannot be placed too late because stresses can rise to a level (40% to 50% of the tensile strength) that leads to microcracking, which has the potential to reduce long-term durability (3, 4) through increased freeze-thaw damage and spalling. Random cracking can also be difficult and expensive to correct.Guidance from many national agencies is limited in determining the timing of saw cut placement. For example, the American Concrete Institute (5) recommends that "the joints should be sawed as soon as practical wherein the concrete should have hardened enough." The Indiana Department of Transportation standard specification 503.03 specifies that the saw cut should be placed between 2 and 12 h for transverse and D-1 joints (6). It also recommends that saw cuts should be placed for longitudinal joints as soon as pavements are "sufficiently hardened." Currently, the timing of saw cut placement is mainly determined based on the saw operator's experience, the indentation of the operator's boot heel, or a scratch on the surface of the pavement. Saw cut timing is also based on the project length, size, and the contractors' resources (7 ).Small, but significant, steps have been taken to remove the guesswork from the saw cutting of concrete pavements. Several computer programs have been developed (8, 9) to predict early-age stress development in portland cement concrete pavements (PCCP). However, many of these do not consider saw cutting. HIPERPAV II (10) recently added a feature to address the timing of saw cutting. Because the timing and depth of a saw cut are two interrelated factors (11), further work is still needed to reliably determine the timing and depth of saw cuts. Gaedicke et al. (11) performed tensile wedge tests to determine the influence of concrete mixture proportions and aggregate size on the fracture toughness development in concrete as it relates to saw cutting.When a saw cut is placed in a concrete pavement, the classical strength of materials approach to predict the average section stress fails to capture the stress concentration that develops at the tip of the saw cut. The cracking behavior of concrete pavements can therefore be better described using principles of nonlinear fracture mechanics (11,12).This paper presents results from a 4-year study. The first portion of this study monitored construction operations for numerous field cases (7 ). The paper describes the use of finite element software to develop a simple methodology to determine the depth and the timing of saw cutting. Results from the finite element analysis were also compared with field observations. RESEARCH OBJECTIVEThe main objectives of this paper are as follows:1. To introduce a strength reduction factor to determine the saw cutting time window and depth using the stress distribution from an uncut pavement; Stresses develop in portland cement concrete pavements (PCCP) shortly after placement when the volume changes associated with temperature change...

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The restrained shrinkage ring test has been used to assess the shrinkage cracking potential of concrete mixtures and to assess the influence of mixture proportions, admixtures, and the use of fiber reinforcement on shrinkage cracking. However, further work is still needed to link the shrinkage cracking performance of fiber reinforced concrete as evaluated using the restrained ring test to the behavior of these mixtures in different size concrete elements in the field. This study used finite element analysis to investigate the cracking behavior of restrained rings of different sizes. The results indicated that due to damage localization the crack widths that develop in the restrained rings are greatly dependent on the size of the restrained ring, the degree of restraint, and the softening behavior of the concrete. This size dependence would influence the performance that would be expected in the field.