The use of high-strength concrete in precast factories is a common solution to attain larger spans and columns with a higher load bearing capacity. Taking into account the cost for transform the mold turnover in the precast line, it is economical to alter the concrete composition and the amount and size of reinforcement to attain the higher requirements. In collaboration with a precast factory, a test program was carried out to reveal the influence of concrete composition and curing temperature on material properties. The goal of the project was to predict the strength evolution of the material, using conventional maturity functions. Therefore, different concrete compositions were used, varying from concretes normally used on construction site, to high-strength concrete. Different curing temperatures were considered. The paper presents the evolution of the compressive strength in time, taking into account different parameters as well as the evaluation of existing maturity functions. Among others, the maturity functions of Plowman, of Kee, of Freiesleben -Hansen and Pedersen and of Carino are investigated. Especially the model, proposed by Carino predicted the strength evolution adequately.

The properties of concrete containing foundry sand as a partial replacement of fine aggregate were investigated. Three types of sand used in foundries were considered, the white fine sand without the addition of clay and coal, the foundry sand before casting (blended), and the foundry sand after casting (spent). The standard sand (Class M) was partially replaced by (O%, 25%, 50%, 75% and 100%) these types of sand. Thirteen concrete mixtures were employed to conduct this study. Concrete strength up to 90 days and length change (drying shrinkage and expansion) up to 60 days were determined. As the replacement level of standard sand with sand used in foundries increased, the strength of concrete decreased. Concrete containing white sand showed somewhat similar strength to those containing spent sand at all replacement levels. The presence of high percentage of blended sand in the concrete mixture caused a reduction in strength as compared with concrete incorporating white sand or spent sand. The increase in strength was not observed at low replacement levels (less than 50%). The length change of concrete increased -as the replacement level of standard sand with the three types of sand increased. Drying shrinkage values were higher in concrete containing spent sand and lower in concrete containing white sand. Expansion was generally lower in concrete containing white sand as compared with the other two types (blended and spent) at a low sand replacement level of 25%; and, different trend was obtained at higher levels.

Recycled aggregate concrete was used as structural concrete at site under the strict quality control system especially on water content in concrete. Two innovative methods were applied for this project: one is the rapid test method for water absorption of aggregate, and the other is the continuous real-time monitoring of water content of freshly mixed concrete at site using a radio isotope (RI) moisture meter. With regard to the rapid test method for water absorption of aggregate, hot water and pressure were applied for the test. By the rapid method, test results could be obtained within two hours. This method is very useful in water content control of concrete produced at mixing plants, especially for concrete with recycled aggregate, water absorption of which generally fluctuates more than that of normal aggregate. As for the water content control using RI moisture meter, water content of freshly mixed concrete transported to the site was being continuously monitored during pumping by a meter attached to the transporting pipe of the concrete pump. Neutron radiation intensity measured varies with the water content of concrete. Every 120 seconds, measurements were used for running mean of water content. According to some experimental studies on this method, standard deviation of the water content of concrete is about 3 kg/m3. In this paper, outline of above-mentioned methods and their application at site are described.

Biogenic sulphuric acid corrosion is a phenomenon which occurs mainly in sewer pipes. The process consists of four stages: the reduction of sulphate to sulphide; the transition of sulphide to hydrogen sulphide gas in the sewer atmosphere; the re-oxidation of the sulphide gas to sulphuric acid in an oxidizing environment of the sewer pipe and finally concrete attack by sulphuric acid. Different models are developed to predict the sulphide formation and the corrosion rate. The model of Pomeroy, according to which the rate of sulphur production and the rate of corrosion can be calculated, is used in this paper. Different parameters are taken into account and case studies are described. Comparison of the calculated corrosion and the measured corrosion indicates the accuracy of the formula. Additional, a sensitivity study is carried out on the formulae to distinguish the influence of the different parameters. A realistic variation of the different parameters is made, based on measurements at the inlet of purification plants. The most influencing parameters for the model were the temperature, the BOD-content and the pH-value of the waste water, the depth of flow and the detention time.

The maturity approach has been used conventionally to model temperature effects on the development of concrete compressive strength. Its application to concrete technology, however, goes far beyond simply estimating compressive strength. When the maturity approach is based on cement hydration kinetics, it can be applied to any concrete property related to the extent of cement hydration. In this study, the application of the maturity approach to model the development of various concrete properties was investigated. In addition to compressive strength, other properties evaluated included degree of hydration and ultrasonic pulse velocity. Hyperbolic equations were investigated for the development of each model. Different values of apparent activation energies (Ea) were calculated according to the procedure in ASTM C 1074. It was concluded that E, is an indication of the thermal sensitivity of the concrete property investigated. The calculated value of E, depends on the specific property and the maturity model used.