There are a lot of errors in the placing of concrete which may occur in concrete construction having different reasons. So we are going to discuss separately.
In concrete construction works, we use different types of cement.
Ordinary Portland cement (OPC) and Portland Pozzolana Cement (PPC) are available in the market but both have different early age gaining strength. The Pzzolaana Portland cement (PPC) gain strength slowly and the formwork may delay from 14 to 21 days. If the formwork was removed after 14 days the error may occur.
Silt and dirt present in aggregate causes cracks in concrete, but no serious checks are made on these things at the site. The stored coarse aggregates allow the silt to settle at its bottom layer. In the construction site, we often considered that the top and bottom layers of coarse aggregate were the same (But they are not) and both give the same strength in concrete. So if we use the dirty aggregates error in concrete construction may occur.
3- Water – Cement ratio
So to achieve the strength and durability of the concrete the water-cement ratio must maintain. Less water more strength and more water less strength. So sometimes at the site construction, the labour may add more water to increase the workability. so the error in construction occurs because they exceed their design w/c ratio.
4- Mixture types and mixing time
In drum mixing concrete the mixing time is the 60s. It is not fully understood that this mixing time depends on the type of mixer and the inclined axis of mixers. The Pan mixers take the 30s, The tilting drum mixer may take 120s. so if the concrete was not a fully mixed error may occur.
5- Placing by mortar plans
At the site, the mortar pans may dump on the reinforcement directly to effect easy discharge of concrete. so in this way, the coarse aggregates and mortar may separate and the error occurred.
The reinforcement is always checked before the concrete pouring. Many types of errors occurred in the construction sites.
Just take one example, The spacing of main bars was mention 6″ and at the site, the bars were spaced 8″ so an error occurred.
Maintaining the proper lining and level in the formwork is very important. The strength of formwork must greater than the concrete and other moving loads present on the slab. If less strength formwork was used the error may occur.
The vibrator was used at the site for the compaction purposes. If the vibrator was used more at the same place segregation in concrete may occur. so if you use the vibrator at the same place error may occur.
If a large amount of water was used in concrete. It affects the concrete and slurry comes on the top which leads to shrinkage cracking and crazing on top.
if the proper curing was not done the hydration reaction may not proceed properly. so if the curing was not done the cracks may develop.