This paper presents the findings of an investigation using the finite-element method to predict the distribution of temperatures within a hydrating massive concrete element. The temperature distribution produced by the finite-element thermal analysis of the model is used in the finite-element structural analysis to quantify the maximum allowable internal temperature difference before cracking will initiate in the concrete. To verify the results obtained in the finite-element model, four different mixes of concrete, typical for use in mass concrete applications in Florida, were produced and each mix was used to make two large-scale 1.07 m×1.07 m×1.07 m (3.5 ft×3.5 ft×3.5 ft) concrete blocks. The mechanical and thermal properties of early age concrete used values obtained experimentally from the concrete used to construct the four sets of blocks. The temperature distributions produced by the model were shown to be very similar to those measured in the experimental blocks. Results suggest that ...

In this research, the ability of pervious concrete pavement material to reduce pollutant concentrations and purify water was investigated. This project mainly aims to study the ability of pervious concrete pavement material to reduce pollutant concentrations such as those in diluted sulfuric acid, seawater, and motor oil. The results demonstrated that the ability of pervious concrete pavement material to reduce pollutant concentrations and purify water was effective in diluted sulfuric acid, artificial seawater, and motor oil tests. After flowing through pervious concrete pavement, a diluted sulfuric acid solution (pH value 2.0) could dramatically increase its pH value to approximately 7.0. A pervious concrete pavement system could greatly decrease the content of an artificial seawater solution (salinity 36%) to about 1%, and the oil content of motor oil combined with certain types of water could also be significantly decreased to 1%. The study demonstrates that pervious concrete pavement holds po...

Three-dimensional finite element (FE) thermal and stress models were created to compute the temperature evolution, thermal stress and potential of cracking in a segmental concrete box girder segment during construction. User-defined subroutines were developed in the ANSYS program to activate the degree of hydration-dependent heat rate and material properties, and creep behavior in the thermal and stress calculations. The developed FE model was verified with experimental measurements of a concrete cube. Adiabatic temperature rise, together with compressive strength and splitting tensile strength for a high-strength concrete mix typically used in construction of box girders were tested and incorporated in the subroutines. The effect of casting time and placement season (summer and winter), initial concrete temperature change, and insulation on the risk of cracking in a cast-in-situ box girder segment at early ages was investigated using the proposed model. The results indicate that the temperature difference between the segment’s middle and the gate corner is very large leading to a high cracking risk. Use of an insulation material such as blankets along with casting concrete at the nighttime would significantly lessen the thermal tensile stress and thus could reduce cracking risk in the segment.

This paper presents the findings of an investigation on thermal behavior of mass concrete footings placed directly on soil using finite element analysis. A three-dimensional finite element model was developed to predict temperatures in a mass concrete footing–soil system and to assess cracking potential of the concrete at early age. Two bridge pier footings constructed in Florida were monitored for temperature development, and the measured temperatures were compared with the computed temperatures from the finite element model. The results show that the temperatures predicted by the model closely agree with those measured in the field. Several soils with varying thermal resistances were modeled in this study in order to find out which soils can be used as an insulator for mass concrete footings so that an insulation layer would not be needed at the bottom of the footings. The results suggest that dry sand and dry clay provide good insulation at the bottom of mass concrete footings, and soil with an R-value of 0.072 per m or greater (or thermal conductivity of 0.35 W/m-K or lower) would provide adequate insulation at the bottom of concrete footings to prevent early-age cracking in the concrete.

The research discussed in this paper is a subset of a bigger, NSF funded research project that is directed at investigating the use of sustainable building materials. The deployment context for the research is the hot and humid climate using selected cases from the East African region. The overarching goal for the research is advancing the structural use of earth-based technologies. Significant strides can be made through developing strategies for countering the adverse factors that affect the structural performance of the resulting wall, especially ones related to moisture dynamics. The research was executed in two phases. The first phase was a two-day NSF supported workshop which was held in Tanzania in July 2009. It provided a forum for sharing best practices in earth-based building technologies and developing a research and development roadmap. The priority research areas were broadly classified as optimizing the physio-mechanical properties of earth as a building material and managing socio-cultural impediments. In the second phase of the research, the authors collaborated with researchers from East Africa to conduct experimental work on the optimization of physio-mechanical properties. The specific research issues that have been addressed are: (1) characterizing the chemical reactions that can be linked to deterioration triggered by hygrothermal loads based on the hot and humid context, and; (2) developing a prototype for a simpler, portable, affordable and viable compressed brick production machine. The paper discusses the results from the characterization work that ultimately will be used to design bricks that have specific properties based on an understanding of how different stabilizers affect the hydration process. It also describes a cheaper, portable and more efficient prototype machine that has been developed as part of the follow-up research activities.