Advances in Evaluation of Lignosulphonates as Concrete Admixtures

The development and evaluation of chemical admixtures requires experimental verification of many admixture samples in the laboratory prior to testing the most promising formulations in concrete. Since quantities of new admixture formulations are usually limited, it is necessary to carry out small-scale tests on fresh cement pastes and mortars. The large number of test methods used by individual researchers makes it difficult to compare results from different laboratories. In an attempt to solve this comparability problem, an advanced methodology for testing of water-reducing admixtures has been developed and is discussed in this paper. This methodology is based on studying the properties of fresh cement-water systems, namely pastes and mortars, with or without the addition of a chemical admixture. It includes and modifies some traditional tests such as the Vicat test for cement pastes and the flow test for cement mortars plus some more recently developed tests such as the mini-slump test. It also includes some new test methods such as the torque test and the mini-flow test. The applicability of the new set of test methods was examined during the evaluation of lignosulphonates as water-reducing admixtures for concrete. The determination of rheological properties, air entrainment and set retardation was conducted on cement pastes and mortars. The values describing the plasticity/fluidity, air content, and time of setting were obtained by different methods and under different conditions. The results were then compared and their interpretation is discussed. The methodology presented here is suitable for preliminary evaluation of concrete admixtures. Incorporation of these test methods into national and international standards is suggested.