Cement-the building construction glue.

It is an open secret that the main reason why human beings live together in a community is because they are not self-sufficient. Living in a community or city makes it easier to acquire goods that one lacks the capacity or competitive advantage to produce. What strengthens and holds together the fabric of this community is virtue like honesty, industry, fortitude and bravery. The opposite scenario-a society where people look down upon virtue, if taken to its logical extreme is a nightmarish gangland anarchy. That is why virtue is critical and should never be taken lightly because it makes a big difference in the quality of life people lead.

In building construction, cement works more or less like virtue holding building parts together by binding foundation and wall courses together permanently, one brick at a time. Besides that, cement also gives additional strength and durability to structures as well as an eye catching finish.

Cement is a grey powder with a fascinating characteristic that makes it essential in building construction. A chemical reaction is set off, when it’s mixed with water, which makes the cement material to hold fast together and  harden with passage of  time. This is why it’s used to make mortar    for boding foundation and wall courses as well as making concrete.

Depending on the construction specifications, the Mason may use Lime or Portland cement. The Lime may be used on its own as a bonding material in mortar- to   give the mortar higher water retention capacity   and increase its cohesion so that it can be spread more easily. However Lime is also used in the manufacture of Portland cement .In other words, cement is lime that has undergone further refining processing during which time other ingredients are added to it.

Cement is used in variety of ways like in making mortar (mix of sand, cement and water), making Ballast (mix of cement, gravel and water), or mixing concrete (mix   ballast, sand and water)-to name a few applications.

Lime.

Lime like Cement is manufactured from Limestone rocks. These rocks   are found in handsome supply in Makueni and Coast counties in Kenya, explaining why all cement factories are located in these regions.

Lime is manufactured by changing calcium carbonate (crushed limestone rocks) to calcium oxide.

CaCO3 ——————–950°C————————–⇒CaO   +      CO2

Calcium carbonate                                                                                             Lime +     Carbon dioxide

The crushed limestone rocks is burnt at temperature of 950 degrees Celsius to produce Lime and carbon dioxide as a byproduct. When water  is added to  lime  the  chemical reaction produces  hydrated  lime  powder  which is  calcium hydroxide.

CaO   + H2O——————————————⇒Ca (OH) 2

Lime   + water                                                                                    Calcium hydroxide

Lime is used in mortar and in manufacture of certain aerated concrete blocks. Mortar  made  up  of  lime is  flexible  and  the presence  of  un-carbonated  lime   may make  minor cracks  in finished work  to  heal  by  the action of  rain water. This  because  lime  hardens   by  absorbing  carbon dioxide  from the air  which  progressively  reverse  the process used to manufacture  it – converting   calcium oxide  to  calcium carbonate.

Hydrated  lime   react  with moisture  and  carbon dioxide  from the air  and should  be  kept in   a  sheltered cool  dry  room and  used  while fresh  from  opened packaging.

Cement

The common Cement you are familiar with, is often referred to as Portland cement (although there are other cement types that do not qualify to be called as such). The name Portland is derived from Portland stones (which is a type of limestone rocks) mined   in the isle of Portland, Dorset-England. The Portland stones has been used extensively in   major public buildings in Great Britain. This begs the question :how did this name come to be  applied to common cement? .Well the name Portland cement was , initially used  to   market and promote   cement   by likening  to Portland stones-a historically prestigious building material that was  selling  like  hot  cakes. With passage of time, cement became a household name and a product of necessity in building construction. As a result the original meaning and purpose lost their significance but the name stuck.   Therefore it fair to say that, there nothing “Portland” in any Portland cement. It is just name-end of that discussion!

Cement is a child of hydrated lime-that is to say it was developed from the Lime. The raw material used to make cement  are limestone or chalk, shale and clay   which   are low cost and widespread -making cement a low cost material. The  manufacturing process  involves  burning  crushed limestone or chalk in kiln to  eliminate carbon dioxide  and  then adding  to the powder  clay  and  iron oxide  plus  other  minor  mineral  like sodium and  potassium.

Portland cement is hydraulic or uses water to work. When it is  mixed  with water  it  forms  a paste    which sets and  hardens  as  a result  of  chemical  reactions  between its  constituent compounds and  water. This setting and hardening does not depend on drying but on the chemical reaction. In fact Portland cement will harden under water. Additional water is needed to make it easy to work with cement when aggregated are added to it.

To prevent corrosion of reinforced steel   in concrete, manufacturer will limit the amount of sodium and potassium oxides in cement they produce and sell.

Water proof cement.

This  is manufactured  by  adding hydrophobic materials such  as  stearates  and  oleates  which works  by   coating  the surface of  pores and  by  surface tension effects which  discourage penetration of water molecules. Also the compounds reduces the water –cement ratio which in turn reduces the pore sizes in concrete. This cement is used in making underground water cisterns among other uses.

Price and uses

As already mentioned above, cement is used to make mortar for binding brick, stone   and concrete block works. Again cement is also used in concrete block manufacture as well as a plastering finish on floor and walls.

The price of cement in Kenya range between Kshs 500   to Kshs 800 per bag. Common Portland cement brands in Kenya   are Bamburi Cement, Portland cement, Rhino cement   and Savannah cement.

©Copyright 2017 eastafricaminihardware.com

Sources:Material  for Architects and Builders by Arthur Lyons -PhD.

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