The major building element used in construction is cement. It acts as a binding material for the ingredients used in concrete. The durability of the concrete structures relies on the grades and the types of cement used in construction. The overall strength and longevity of the structure count on the physical and chemical properties of cement.
In today’s blog from Brick & Bolt, you are going to explore the different cement properties in more detail.
What is Cement?
Cement is a very fine powder made up of limestone (calcium), sand or clay (silicon), bauxite (aluminum), and iron ore, and may include shells, chalk, marl, blast furnace slag, slate. There are different types and grades of cement available for various construction needs.
Chemical Composition of Cement
Ordinary Portland cement is produced with the combination of four main compounds: tricalcium silicate (3CaO · SiO2), dicalcium silicate (2CaO · SiO2), tricalcium aluminate (3CaO · Al2O3), and a tetra-calcium aluminoferrite (4CaO · Al2O3Fe2O3). This includes small amounts of uncombined lime and magnesia, as well as alkalies and negligible amounts of other
Physical Properties of Cement
The following are the major physical properties of cement:
Fineness
Fineness defines the particle sizes of cement. Good cement’s required fineness is achieved by grinding the clinker in the last step of the production process. The hydration rate of cement is directly proportional to its particle size. The higher surface area-to-volume ratio will result in a larger accessible area for water-cement interaction per unit volume. The cement fineness ratio varies based on the type of cement: Ordinary Portland cement has a fineness ratio of 10 percent, low-heat cement has 5 percent, and rapid hardening cement ranges from 3 to 5 percent.
Soundness
The ability of cement to resist shrinkage after hardening is referred to as its soundness. Good quality cement retains its volume after setting without delayed expansion caused by excessive free lime and magnesia. The Le Chatelier and autoclave tests are used to determine the soundness of cement. The cement should not show an expansion of more than 10 mm in the Le Chatelier test, and the expansion in the autoclave test should not exceed 0.8% of the original length of the specimen.
Consistency
Cement consistency refers to the viscosity or flowability of the cement paste. The standard consistency of cement is 26-33% by weight of dry cement.
Strength
There are three types of cement strength – compressive, tensile and flexural. Different factors influence the strength of cement, such as water-cement ratio, cement-fine aggregate ratio, curing conditions, specimen size and shape, moulding and mixing, loading conditions, and age. The compressive strength of cement is typically tested using the Cube test or Cylinder test. The Split Tensile Strength Test and Direct Tensile Strength Test are used to assess tensile strength, while the Flexural Test, also known as the Modulus of Rupture Test, is used to measure the flexural strength of cement.
Setting Time
The setting time of cement is described as the time it takes for the cement to transition from a liquid to a plastic state and then to a solid state. This setting time can vary depending on factors such as the fineness of the cement, the water-cement ratio, the chemical composition, and the admixtures. The setting time of cement is measured using the Vicat Apparatus Test and is categorised into initial setting time and final setting time. The initial setting time, which is the period for the cement to transition from a liquid to a plastic state, should be around 30-45 minutes. The final setting time, marking the full transition to a solid state should be approximately 10 hours.
Heat of Hydration
When water comes in contact with the cement, a reaction takes place, and energy is generated, this process is known as heat of hydration This heat of hydration generates heat, which can influence the quality of the cement. It can also help keep the curing temperature during cold weather. However, when high heat is generated, particularly in large structures, it may cause unwanted stress.
Loss of Ignition
Weight loss occurs when a cement sample is heated between 900 and 1000°C (or until a consistent weight is attained). This weight loss due to heating is estimated as a loss of ignition. Pre-hydration and carbonation may result from improper and prolonged storage or adulteration during transport or transfer, both of which are detectable by increased loss of ignition.
Bulk Density
Bulk density is the mass of cement per unit volume. Cement density varies depending on its composition percentage. Typically, cement’s density ranges from 992 to 1249 kg/m³. The average bulk density of cement is 1440 kg/m3
Specific Gravity
The specific gravity (or relative density) of cement is the ratio of the mass of cement to the mass of the reference material, which is commonly water. Specific gravity is commonly used in the calculations of mixture proportions. The relative density of Portland cement is 3.15, and portland-blast-furnace-slag and portland-pozzolan cement have specific gravities of about 2.90.
Chemical Properties of Cement
The following are the chemical properties of cement:
Tricalcium Silicate (C3S)
The early strength growth and first setting of the cement depend on C3S, which also induces quick hydration and hardening.
Dicalcium Silicate (C2S)
Dicalcium silicate in cement aids in strength gain one week later than tricalcium silicate, which aids in strength gain earlier.
Alumina
Alumina has a good resistance to chemical attack. Excess alumina reduces cement strength and increases setting time. High alumina cement (HAC) is utilised in industrial structures to withstand chemical attacks.
Tricalcium Aluminate (C3A)
Cement with a lower C3A (tricalcium aluminate) content is more resistant to sulfates. Gypsum is added to cement to inhibit the hydration of C3A, as this reaction releases a significant amount of heat during the initial phases of hydration. C3A contributes only a small degree of strength to the cement. In Type I cement, which may contain more than 8% C3A, the SO3 (sulfur trioxide) content can be up to 3.5%. For Type II cement, which has less than 8% C3A, the maximum SO3 content is 3%.
Ferrite(C4AF)
Ferrite (C4AF) is a fluxing agent. It lowers the raw materials’ melting point in the kiln from 3,000°F to 2,600°F. Despite its quick hydration, it has little effect on the cement’s strength.
Magnesia (MgO)
In dry process plants, magnesia is used as a raw material in the production of Portland cement. A small amount of magnesia can provide the cement strength, but too much of it can cause the cement to expand and become unsound. MgO-based cement production also results in lower CO2 emissions. The maximum MgO level for any cement is 6%.
Calcium Sulfate
Gypsum contains calcium sulfate, which accelerates or retards the initial setting time of cement.
Iron Oxide
The iron oxide aids in the blending of raw components during the cement manufacturing process and gives the cement colour.
Sulfur Trioxide
A greater amount of sulfur trioxide affects the soundness and expandability of cement. As a result, the percentage of sulfur trioxide should not exceed 2%.
Alkalies
Efflorescence occurs when there is an excess of alkalies. So the percentage of alkalis in cement should be kept to a minimum. The cement’s alkali content is determined by the proportions of potassium oxide (K2O) and sodium oxide (Na2O). Controlling the cement’s setting time can be challenging when the cement contains a lot of alkali. When low-alkali cement is used with calcium chloride in concrete, discolouration may result. Ground granulated blast furnace slag is “activated” by adding alkalis to slag lime cement, which prevents it from being hydraulic on its own. The formula Na2O + 0.658 K2O yields an optional limit of 0.60% for the overall alkali content. The presence of alkali oxide is limited to 1%; otherwise, it has a negative impact on the structure’s strength.
Lime
Its principal element, lime, influences cement’s strength and setting time. The percentage of lime should be added cautiously; otherwise, it will affect the soundness of the cement (expand) and cause it to disintegrate.
Cement is a major building material, that acts as a binding agent in concrete, Its properties influence the strength, durability, and longevity of concrete structures. Understanding the various physical and chemical properties of cement is essential for selecting the appropriate cement type and ensuring the desired performance in construction projects.
You can consult the highly reputed construction companies in Bangalore, like Brick & Bolt, to select the most suitable type of cement for your project after analysing your structure’s requirements and the physical and chemical properties of cement. Moreover, they provide the best quality craftsmanship, 470+ quality checks, and a construction cost calculator for free for your construction projects.