Abstract
Rheological behaviour of some products based on chemical modified starch, with characteristics proper to retarding additives for concrete designed for cementation of the big depth wells, was investigated. With that end in view, rheological tests of several pastes obtained from products of the hydroxypropylstarch type were carried out. Maintaining, at pastes preparation, the concentration of 10% additive, proved as being the most efficient in use, shearing strain tests were performed at 20°C, 40°C and 60°C versus keeping time of pastes, namely, 24 h and 48 h from preparation time. At the same time, influence of the disodicphosphate and urea additions over rheological pastes was investigated versus the same parameters. Based on the experimental results obtained, the mathematical models describing rheological behaviour of the tested additives, within a large range of external stress and temperature, were elaborated.
Keywords: hydroxypropylstarch; rheological equation; retarding additives; concrete for wells