Apparent diffusivity model for concrete containing supplementary cementitious materials

Concrete’s resistance to chloride diffusion is one of the primary factors governing the concrete structure service life and life-cycle costs. This paper presents a new model developed for estimating the apparent concrete diffusivity based on the mixture proportions, cementitious materials used, and concrete age. The model includes the effects of supplementary cementitious material types commonly found in other service life models such as fly ash, ground-granulated blast-furnace slag, and silica fume. Also included are ultra-fine fly ash and metakaolin, which were not available in previous service life models. For validation of the model, chloride profiles have been measured on concrete blocks exposed daily to seawater for 25 years at the Treat Island, ME concrete exposure site. Concrete mixtures tested as part of the validation dataset contained up to 80% ground-granulated blast-furnace slag, 25% fly ash, or 20% silica fume, and were compared against the predicted values and are presented in this paper

Modeling hydration of cementitious systems

Concrete performance, including strength, susceptibility to delayed ettringite formation, and residual stress development are dependent on early-age temperature development. Concrete temperature prediction during hydration requires an accurate characterization of the concrete adiabatic temperature rise. This study presents the development of a model for predicting the adiabatic temperature development of concrete mixtures based on material properties (for example, cement chemistry and fineness and supplementary cementitious materials (SCM) chemistry), mixture proportions, and chemical admixture types and dosages. The model was developed from 204 semi-adiabatic calorimetry results and validated from a separate set of 58 semi-adiabatic tests. The final model provides a useful tool to assess the temperature development of concrete mixtures and thereby facilitate the prevention of thermal cracking and delayed ettringite formation in concrete structures

Alternate reinforcements for enhanced corrosion resistance in TxDOT bridges: final report

The corrosion of reinforcing steel in concrete is the leading cause of deterioration for reinforced concrete structures, especially bridges exposed to external chlorides. Practitioners and researchers have evaluated and implemented various technologies to combat this problem, including the use of high-performance concrete, chemical corrosion inhibitors, sealers and barriers, and alternative reinforcement. This synthesis project addressed the latter, specifically the use of alternative reinforcement (e.g., fiber-reinforced polymer (FRP) reinforcement, epoxy-coated steel, stainless steel, galvanized steel, etc.) to extend the service life of bridge structures subjected to external chlorides from marine environments or from de-icing salt applications. The primary goals of this project were to (a) review and synthesize published literature, (b) review and synthesize current DOT practice, (c) identify gaps in our current knowledge and state of practice, and (d) provide guidance, based on current knowledge, on how to evaluate and select alternative reinforcement for bridges subjected to external chlorides.Preprin

Research report (University of Texas at Austin. Center for Transportation Research)

"The research described in this report aims to address several of these lingering issues, especially those that are particularly relevant to the state of Texas.

Test Methods for Evaluating Preventive Measures for Controlling Expansion due to Alkali-Silica Reaction in Concrete

This paper provides a critical evaluation of the various methods available for testing the efficacy of measures for preventing expansion due to alkali-silica reaction (ASR) in concrete containing deleteriously reactive aggregate. The ideal test method should be rapid, reliable and capable of determining the influence of aggregate reactivity, alkali availability and exposure conditions. None of the currently available or commonly used methods meet all of these criteria. The shortcomings of the different test methods are discussed and suggestions are made for modifying the concrete prism test and accelerated mortar bar test to make these tests more acceptable.Aggregates Foundation for Technology, Research, and Education (AFTRE)Civil, Architectural, and Environmental Engineerin

Temperature Boundary Condition Models for Concrete Bridge Members

The temperature development of mass concrete elements is strongly dependent on constituent materials and mixture proportions, as well as the formwork type, geometry, and environmental conditions. This paper presents a method to account for the effects of convection, radiation, and shading on the surface temperature of mass concrete. Solar radiation, atmospheric radiation, surface-emitted radiation, and formwork radiation exchange were considered. Wind speed, ambient temperature, and surface roughness were included in the convection model. The model described was incorporated into a mass concrete temperature prediction model. The predicted temperatures were then compared with measured near-surface concrete temperatures. The ability of the model to predict the maximum temperature and maximum temperature difference were also examined. The results show that the model accurately estimates the near-surface concrete temperatures, the maximum temperature, and maximum temperature difference of the 12 concrete members instrumented