Cement is basically fine powder that gets set after a few hours when mixed with water, and then starts hardening in a few days into a solid, strong material. Cement is primarily used to bind fine sand and coarse aggregates together and held them compact in concrete.
There are around 30 types of common cement which can be classified into 5 general categories and 3 strength classes: ordinary, high and very high. In addition to these, some special cements like sulphate enduring cement, low heat cement and calcium aluminate cement are also some more types being produced and sold.
Cement Manufacturing process at a glance:
The quarry is the starting point
Cement plants are usually built and assembled closely either to market or to areas having sufficient quantities of raw materials.so as to cut transportation costs. Basic constituents for cement (limestone and clay) are fetched from quarries in and around these areas.
A two-step process
Cement is generally produced in two steps: firstly, clinker is made from raw materials. Next, the cement is produced from previously made cement clinker. The first step tends to be a dry, wet, or semi-wet process varying as per the state of the raw material.
The required materials are delivered in bulk, crushed and mixed which is fed into a rotary kiln. This is a massive rotating pipe with a length of around 60 to 90 m and 6m in diameter. This huge kiln is heated on 2000°C. It is slightly inclined to allow for the materials to travel across the kiln, where it is rapidly cooled down to 100-200°C.
Four basic oxides while mixed in the right proportion make cement clinker: calcium oxide (65%), silicon oxide (20%), alumina oxide (10%) and iron oxide (5%). These elements mixed homogeneously will combine when heated by the flame at 1450°C. Hence new compounds of calcium and silica are formed which dry to form hydraulic cement.
Here, stage 1 is finished with the end product as clinker
Phase 2: From clinker to cement
The second phase is carried out in a cement grinding mill, which can be at a different location from the clinker plant. Sulphates of calcium and possibly some extra elements as the likes of blastfurnace slag, coal fly ash, natural pozzolanas, or inert like limestone are mixed with the clinker. All the ingredients are ground leading to a fine and harmonized fine articles like powder. Second phase ends here and the cement is now ready to be stored in silos before being dispatched either in bulk or individually bagged.
What is concrete?
Concrete is a hard material made from cement, water, aggregates and may have some admixtures. When it’s fresh, certain workability exists and takes the shape of the same mould into which it is put. When set and reinforced, it has similar strength as stone and resists time, water, frost, motorised constraints and fire. Concrete is typically the crucial material used in all kinds of construction
Types of cement
Portland cement blends
These are found and ready as inter-ground mixtures from cement producers and vendors, but similar making are often mixed from the ground components at the concrete mixing plant.
Portland blastfurnace cement:
This contains almost 70% ground granulated blast furnace slag, and rest is Portland clinker and a small proportion of gypsum. All compositions deliver high ultimate strength, but as slag proportion is hiked, early strength is reduced, while sulphate resistance increases and heat evolution decreases. Perceived as an economic alternative to Portland sulphate-resisting and low-heat cements.
Portland fly ash cement:
Around 35% fly ash can be found in this which is pozzolanic, so as to maintain the ultimate strength. As fly ash addition allows low levels concrete water content, early strength is also easily maintained. If good quality fly ash is available at reasonable prices, this can be an economic alternative to Portland cement.
Portland pozzolan cement
In addition to fly ash cement, this includes cements made from other natural as well as some artificial pozzolans. In regions where volcanic ashes are available, these cements are usually the most common form in use.
Portland silica fume cement.
Adding some silica fume can yield exceptionally high strengths, and cements having proportions of silica fumes from 5–20% are occasionally produced. However, silica fumes are more usually added to ordinary Portland cement at the concrete mixer.
Masonry cements serve the purpose of preparing bricklaying mortars and stuccos, and should never be used with concrete. They are usually complex proprietary mixtures including Portland clinker some likes of include limestone, wet limes, air entrainers, retarders, waterproofers and coloring agents. They are formulated to produce workable mortars which allow speedy and stable masonry work. Subtle alterations in Masonry cement in the US are Plastic Cements and Stucco Cements. These are developed to yield controlled bond with masonry blocks.
Expansive cements: in addition to Portland clinker, expansive clinkers which usually are some sulfoaluminate clinkers, are designed to equalize the effects of drying which is generally witnessed with hydraulic cements. This allows huge floor slabs may be up to 60 m square to be prepared without using contraction joints.
White blended cements are usually made using white clinker and white accompanying materials such as high-purity metakaolin.
Coloured cements are used mostly for decorative purposes. In some benchmarks, the addition of colorants to produce "coloured Portland cement" is allowed. In some other standards where pigments are not allowed constituents of Portland cement, the coloured cements are sold by the name of "blended hydraulic cements".
Very finely ground cements are produced from mixing cement with sand, slag or other pozzolan types of minerals that are finely ground together. Cements prepared thus can have the similar physical characteristics as normal cement but with around 50% less cement particularly specifically due to their increased surface area for the chemical reaction. Even with rigorous grinding they can use at least up to 50% less energy to fabricate than ordinary Portland cement.