PCI Journal Paper Title: A Precast Segmental Substructure System for Standard Bridges

This paper focuses on improving bridge substructures by developing attractive and rapidly constructed substructure systems for short- and moderate-span bridges. The importance of improved substructure design is discussed. A review of current cast-in-place and precast concrete substructure systems is presented. A specific proposal for a precast segmental substructure system is described including methods of fabrication and erection. The goal of this system is to improve aesthetics and reduce construction time for standard bridges. Reduced construction time leads to important safety and economic advantages when traffic disruption or rerouting is necessary. Precasting would result in an increased use of high performance concrete and will bring improved substructure durability. Recommendations are made for standardization of precast substructure systems.

The maturity method accounts for the effect of curing temperature on the strength development of well-cured and consolidated concrete. This paper describes an investigation of the accuracy of the maturity method to estimate the strength when different cementitious systems are used. Mortar cubes, made from Type I cement and various replacement levels of Class C fly ash, Class F fly ash, and ground-granulated blast-furnace slag, were cured at isothermal curing temperatures of 8, 23, and 40°C . The amount of long-term strength reduction, due to curing at high temperatures compared with curing at room temperature, is influenced by the type of cementitious system used in the concrete mixture. Based on the strength results of these mortar cubes and the procedure outlined in ASTM C 1074, datum temperature and activation energy values were determined for these cementitious systems. The ability of the equivalent age maturity method to accurately estimate the strength is significantly influenced by the composition ...

The effects of fluctuating temperatures on the setting times of concrete mixtures made with different water-to-cement ratios, supplementary cementing materials (SCMs), and SCM dosages are evaluated in this paper. Initial and final set times of the concrete were determined with penetration resistance testing. Wet-sieved mortar samples were placed in hot and cold water baths that cycled over 24 h between temperature ranges of 32– 41°C and 4– 13°C , respectively. The control samples were cured at temperatures between 20 and 24°C . Results show that Class F fly ash will slightly retard setting, ground granulated blast furnace slag will slightly accelerate setting, and Class C fly ash will significantly increase setting times. It is shown that the equivalent age maturity method may be used to estimate setting times of concrete samples cured under fluctuating temperatures. Activation energy values are recommended for use with the equivalent age maturity method to predict setting.

Early-age cracking in bridge decks is a severe problem that may reduce functional life of the structure. The effect of lightweight fine aggregate on the cracking tendency of bridge deck concrete was evaluated using cracking-frame testing techniques. Water for internal curing is provided by incorporating prewetted absorptive lightweight aggregate (LWA) into the mixture during batching. The absorbed water within the LWA is desorbed at early ages as hydration progresses. The release of the internal curing water increases cementing material hydration and reduces capillary stress caused by self-desiccation. Cracking frames measure the development of stresses due to thermal and autogenous shrinkage effects from setting until the onset of cracking. Restrained concrete specimens were tested under temperature conditions that match those of an in-place bridge deck and under isothermal curing conditions to determine the stress development due to autogenous shrinkage. Internal curing from LWA increased the ti...

Early-age cracking can adversely affect the behavior and durability of bridge deck concrete. Cracking of hardening concrete occurs when the induced tensile stress exceeds the tensile strength of the concrete. The development of in-place stresses is affected by the shrinkage, modulus of elasticity, coefficient of thermal expansion, setting characteristics, restraint conditions, stress relaxation, and temperature history of the hardening concrete. Tensile strength increases as the hydration of the cementitious system progresses. Rigid cracking frame (RCF) testing techniques capture the combined effects of modulus of elasticity, creep and relaxation, coefficient of thermal expansion, thermal conductivity, autogenous shrinkage, and tensile strength on the cracking potential of a mixture in a specific application. This paper describes an experimental evaluation of the effect of supplementary cementing materials, water-to-cement ratio (w/c), and placement temperature conditions on the early-age cracking tendency of bridge deck concrete through the use of RCF testing techniques. Specimens were tested under temperature conditions that match those in an 8-in.-thick bridge deck to explore early-age cracking mechanisms. The laboratory testing program revealed that the placement temperature and curing temperature significantly affected the time to cracking of all the mixtures. Use of either fly ash or ground-granulated blast-furnace slag was effective in reducing the heat generation and rate of stiffness development in bridge deck concretes and thus in significantly reducing restraint stresses and delayed the occurrence of cracking at early ages. A decrease in w/c resulted in increased stresses, and it accelerated the occurrence of cracking at early ages.