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What is the purpose of applying spatterdash before rendering and plastering?

Spatterdash is a mixture of one part of cement to one and a half parts of coarse sand with enough water. The mixture is thrown forcibly onto the wall so that the impact removes the water film at the interface between spatterdash and the substrate leading to the improvement in adhesion.

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What is the difference between no-fines concrete, lightweight concrete and lean concrete?

Pervious concrete is sometimes called “no fines” concrete. It is designed with high porosity and allows water to pass though. It is commonly used in concrete pavement so as to reduce surface runoff and allow the recharging of ground water. The high porosity is achieved by a network of interconnected void. “No fines” concrete has little or no fines and contains just enough cement paste to cover the surface of coarse aggregates while maintaining the interconnectivity of voids.

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What is the difference between dry-mix method and wet-mix method in shotcrete?

Shotcrete is not a special product of concrete and it is not a special method of placing concrete. In dry-mix method the dry cementitious mixture is blown through a hose to the nozzle, where the water is injected immediately. The dry-mix method appears to be better for low volume placements. The nozzleman should pay great attention in adding the necessary amount of water during shooting operation.

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What are the potential problems of using liquid nitrogen to cool concrete?

Based on the results of past research, there is minimal impact on the properties and performance of concrete by liquid nitrogen (LN). The addition of liquid nitrogen appears to decrease the slump value of fresh concrete. However, the slump loss is not caused by liquid nitrogen but by previous hot concrete mix, i.e. the slump of LN-cooled concrete is the same of original hot concrete. Liquid nitrogen can also be observed to extend the setting time of concrete.

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Should on-site addition of water to fresh concrete be allowed?

The addition of water to fresh concrete in truck mixer upon arrival at the location of concrete is allowed only if some design mixing water is held back during initial mixing stage. Addition of water in excess of design mixing water would definitely cause an increase of water cement ratio leading to a reduction of concrete strength.

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