The hydration of cement and water is an exothermic reaction capable of generating significant amounts of heat. Unaccounted for, the heat generated can alter the chemical reaction of the cement, producing massive cracks in the hardened concrete that sacrifice the integrity of the structural element. Alternatively, the heat produced can create thermal gradients capable of cracking the concrete and exposing the reinforcing steel to chlorides. To prevent either of these events from occurring, a software program known as ConcreteWorks was created as part of a previous research project funded by the Texas Department of Transportation. ConcreteWorks gives TxDOT engineers, contractors, and inspectors the ability to manage the structural design, mix proportions, and construction processes in order to minimize maximum concrete temperatures as well as temperature gradients. The free program has seen successful on several non-TxDOT projects, however, it has failed to become incorporated into standard TxDOT practices and specifications. The goal of this research, funded by TxDOT, was to promote widespread use and acceptance of the program within the DOT. In pursuit of this goal, a four-hour hands-on training class was developed and taught throughout the state of Texas, construction projects were selected for the use and validation of the software program, and a few modifications were suggested to make the program more helpful and easy to use. This thesis primarily focuses on the results of the validation of ConcreteWorks on mass concrete and precast applications. In total, four precast beams and two columns were instrumented. With regards to existing methods of predicting temperatures, the program was fairly accurate for mass concrete applications. The program was also very useful for precast elements; however, the lack of variables to match the model to the actual structure likely limits the software program from producing a more accurate prediction. / text

Abstract This thesis has shown that the development of the instrumentation necessary to provide in-situ thermal imaging for the determination of homogeneity of concrete is theoretically sound. Drilled shafts are large diameter underground cast-in-place columns that necessarily rely on sound integrity to properly withstand imposed loadings. As a by-product of the most common construction techniques, the entire process is often completely blind whereby the excavation and concreting processes are conducted beneath the surface of the water table (or slurry level). This results in an inability to inspect the final product and in many cases allows anomalous inclusions (soil cave-ins, slurry pockets, etc) to go undetected especially when they are formed outside the steel reinforcing cage. In an effort to gain verification of the as-built, below ground structure, numerous non-destructive test methods have been devised. Each of these methods have merits and drawbacks with regards to the full extent of the tested concrete volume. To further this cause, a new methodology was developed that uses the energy from hydrating concrete to assess the presence or absence of an intact concrete. Therein, the temperature generated by the curing concrete can be measured and correlated to the probable dimensions of the drilled shaft. This thesis outlines the development of the instrumentation capable of making in-situ temperature measurement of drilled shafts to assure the homogeneity of concrete is acceptable. To that end, several configurations of instrumentation approach were tested on varying scales from small lab specimens to full-size field constructed drilled shafts. The bulk of this work was conducted several years before the completion of the thesis and has the benefit of noting later developments. For instance, this study was used to seed future research and led to subsequent FDOT and WSDOT (Washington State DOT) funded research for the express purpose of identifying capabilities of thermal testing in those states. Likewise, present day practice and use of the approach has also been documented.

Heat of hydration is a source of problem in mass concrete since it causes the difference between the inner and the outer temperatures increase excessively, which leads thermal cracks. The first step in fighting against this problem is to keep the initial temperature of concrete as low as possible. From this point of view, Preplaced Aggregate Concrete (in short PAC) is quite advantageous, because the friction taking place among the coarse aggregates during the mixing operation causes the initial temperature of concrete increase. However, since coarse aggregates are not subjected to the mixing operation in PAC method, comparatively lower initial temperatures can be achieved. On the other hand, making PAC by the conventional injection method is quite troublesome, since it requires special equipment and experienced workmanship. Because of this, it would be very useful to investigate alternative methods for making PAC. In this research, a new method for making PAC has been investigated. The new method is briefly based on increasing the fluidity of the grout by new generation superplasticizers to such an extent that, it fills all the voids in the preplaced coarse aggregate mass when it is poured over, without requiring any injection. In the scope of the study, twelve concrete cube specimens, each with 1 m volume, have been prepared / one of which as conventional concrete, seven of which as PAC by injection method, and four of which as PAC by the new method mentioned above. In order to examine the specimens that have been prepared by three different methods from thermal properties point of view, the difference between the central and the surface temperatures of the specimens have been followed by the thermocouples located in the specimens during preparation. Also, in order to examine the mechanical properties of the specimens, three core specimens have been taken from each specimen at certain ages, compressive strength and modulus of elasticity tests have been carried out on these core specimens. As a result of the experiments it has been observed that, the PAC specimens prepared by injection method performed better from thermal properties point of view, but worse from mechanical properties point of view than conventional concrete. On the other hand, the PAC specimens prepared by the new method have performed both as well as the other PAC specimens from thermal properties point of view, and as well as conventional concrete from mechanical properties point of view.