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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.
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.
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.
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.
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.
Dusting refers to the formation of loose powder arising from the disintegration of concrete surface. For dusty concrete surface, they can be easily scratched by nails. The cause of dusting can be related to finishing works carried out before completion of concrete bleeding. The working back of bleeding water to concrete surface produces a low strength layer with high water cement ratio. It may also arise owing to inadequate curing and inadequate protection of freshly placed concrete against rain, wind and snow.
Isolation joints isolate slabs or concrete structure from other parts of structure. The presence of isolation joints allows independent vertical or horizontal movement between adjoining parts of the structure.
Plastic shrinkage cracks are caused by a rapid loss of water from concrete surface before setting of concrete such that the rate of evaporation of surface water is higher than the rate of replacement of upward rising water. Tensile force is developed at concrete surface which forms plastic shrinkage cracks when the concrete starts to stiffen. Plastic shrinkage cracks appear to be parallel to each other with spacing of about 300mm to 1m. The cracks are shallow and generally do not intersect the perimeter of concrete slab.
Curing compound is primarily used for reducing the loss of moisture from freshly-placed concrete and it is applied once after concrete finishing is completed.
