Questions and Answers
Why do we go on providing water to the [dried] CEMENT of a recently built building or any such infrastructure?
This hardening process is called hydration and continues for days long after the cement has firmed up enough to walk on.As hydration continues, the cement gets harder and harder until it reaches its full strenght in 28 days. During this curing the cement heats up from the chemical reactions and it also shrinks or contracts. In order for hydration to continue water must be present if enough water is not present then the hydration process will stop before the cement has had a chance to reach its full rated strenght.Newly poured cement is kept moist so that water is kept available for the hydration process to continue and most importantly to even the temperatures so the cement doesn’t crack. Evaporation is controlled by spraying with water or by covering the cement with materials or coatings which keeps the water from evaporating. During the curing (hydration) process heat is also generated, this heat can cause water to evaporate and halt the curing and cause the cement to crack due to uneven contraction. Neither condition is desirable so the cement is kept cool by spraying water on it.In some large cement pours cement is kept cool and wet by using ice and in some very large pours a cooling water system is cast in place (like what was done on the Hoover dam) After the cooling pipes are no longer needed they are filled with grout.
in Concrete Beams, Columns and Slabs to begin Oxidation process.
adminRust is Ferrous Oxide, this is a compound of Iron and Oxygen. When air gets into the cracks, and makes contact with your steel, oxidation process starts. There is a misconception that water makes steel to rust. It is the oxygen in the air actually. However, water hastens the process of oxidation that’s why we suspect it to cause the rusting.The reason cracks on buildings are:1. Inadequate reinforcement. The bending moment of such elements might be too large that steel inside the element cannot withstand and causes the cracks on concrete.
2. Poor workmanship. During the concreting, there might be some honeycombs which were not treated effectively. The voids inside and outside the concrete weakens the concrete. This is also due to ineffective vibration during the placing of concrete.
3. Cold joints might not have been treated with grouting. Connection of concrete from old pour to new pour should have been treated with cement grout.
4. Lack of waterproofing. The materials which used for waterproofing of the structure is not effective enough to protect the concrete form water seepage
5. Creeping and Shrinkage of concrete. This characteristic of concrete takes long time to happen. Concrete shrinks and creeps with the changing temperature and humidity.
6. Design mix of concrete. Sometimes, during the placement of concrete, the strength of concrete being placed is not in accordance with design strength. Ex. Instead of pouring 5000psi, they pour 3500psi.
7. Others maybe less concrete cover, improper curing of concrete and additional loads might have been put to your structure which were not considered in the design.
I suggest that you check thoroughly whether the cracks you have identified are just hairline cracks or structural cracks for you to do the appropriate repair on your structure. Structural Epoxy injection is the commont method if you found structural cracks on you building.
Masonry construction?What durability problems affect masonry structures and what can be done about them?Looking for a little helpany appreciated, thanks.
adminMasonry construction is inherently durable since it is made of sand, cement, and water (among other things). It is an excellent building material if constructed by experienced masons and properly engineered to resist the loads to which the masonry will be subjected. Masonry may be reinforced or unreinforced. Over time, the mortar joints may need some maintenance to keep out rainwater. Water is the arch enemy of any masonry or concrete construction. Properly designed masonry construction includes reinforcing steel within the voids of the blocks and each cell in which the rebar is to be placed is to be grouted solid with a pea-gravel type of flowable concrete called mortar. Any masonry that supports earth such as retaining walls shall be grouted solid regardless of where the rebar is located. The mortar and grout ingredients and proportions are critical for long term masonry construction durability.If masonry cracks within the block, these cracks should be repaired using epoxy injection and then monitored for future movements.I am not sure of the the specific problem you may be experiencing with masonry.
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