Possibilities of retarding the setting of PROMPT natural cement by dosing lignosulfonates

Abstract

Abstract Roman cement (also Natural cement) is a highly hydraulic binder produced by firing limestone rich in clay minerals. A low firing temperature ranging from 800 °C to 1200 °C is typical for Roman cements. This binder has beneficial functional properties: lower CO2 emissions during production, relatively high strength at a lower bulk density compared to Portland cement, resistance against degradation due to salinity, and better durability. A typical property for this binder is fast setting. This is a problem with the application of natural cement in mortars and concretes, as it significantly shortens their workability time in construction site conditions. The beginning of the setting time of mortars based on PROMPT natural cement can be influenced by retarding additives. Citric acid is currently the most used. Citric acid can negatively affect the properties of hardened mortar and its retarding effect may not be satisfactory. The results of the experimental study are presented in this article, where lignosulfonate-based substances were used as setting retarders. It was investigated that selected types of lignosulfonates are effective as a setting retarder. They have, compared to citric acid, a more pronounced effect of delaying the setting. They also have a significant effect on the strength of the hardened mortar after 28, 56 and 90 days.