Construction

Calcium nitrate, or another non-chloride accelerator. Calcium chloride speeds setting well, but the chloride it adds raises the risk of steel corrosion, so ACI guidance says it should not be used in steel-reinforced concrete, and IS 456 limits the total chloride in reinforced and prestressed mixes. Keep calcium chloride for plain concrete with no embedded steel. Calcium nitrate speeds setting and early strength without adding chloride.

The amount of mixing water they remove. A plasticiser, or normal water reducer, such as one based on sodium lignosulphonate, cuts water by at least 5% at the same workability (ASTM C494 Type A). A superplasticiser, or high-range water reducer, usually based on sulphonated naphthalene formaldehyde or polycarboxylate ether, cuts it by 12% or more (Type F), giving flowing or high-strength concrete. Lignosulphonates can also retard setting at higher doses.

When concrete or mortar must stay workable for longer: ready-mix travelling long distances, hot-weather pours, large or continuous placements that must avoid cold joints, and long pumping runs. Sodium gluconate retards cement at very low doses and also reduces water slightly, while tartaric and citric acids are common retarders for gypsum plasters. Set the dose by trial mixes at site temperature, because an overdose can hold the set far longer than planned.

Usually 1% to 5% of the cement or binder weight. Synthetic iron oxides reach their saturation point at about 5%, so higher doses add little colour, cost more and can lower strength. Always dose by cement weight, not total mix weight, and keep the cement, water content and curing consistent, because they change the final shade as much as the pigment does. White cement gives brighter, cleaner colours than grey cement.