Cement is a very important civil engineering commodity, a growing bonding medium. The report is about the physical and chemical properties of cement, as well as the processes used to check the properties of cement.
Physical Properties of Cement
Similar cement blends used in the building are distinguished by their physical characteristics. Other primary parameters regulate cement consistency. Good cement’s physical properties are focused on:
- Fineness of cement
- Soundness
- Consistency
- Strength
- Setting time
- Heat of hydration
- Loss of ignition
- Bulk density
- Specific gravity (Relative density)
Fineness of cement
The scale of cement particles is their fineness. In the last stage of the cement production process, the requisite fineness of good cement is obtained by grinding the clinker. Because cement hydration level is directly related to the particle size of cement, cement fineness is very critical.
Soundness of Cement
Cement soundness is a hardened paste’s ability to retain its volume after setting. A cement is said to be unsound if it is subjected to delayed destructive expansion (i.e., lack of soundness). Concrete in soundness is due to excessive volume of hard-burned free lime and magnesia. Cement soundness means performance to build on the atmosphere. Unsound concrete stretches the environment too much and produces gaps in the foundation.
Tests:
Cement unsoundness can occur after several years, so tests must be able to determine the ability to ensure soundness.
Le Chatelier Test
Using Le Chatelier Apparatus, this process measures concrete expansion attributable to lime. Around glass slides, cement paste (normal consistency) is taken and submerged in water at 20 + 1 °C for 24 hours. The gap between the markers is calculated and then placed to steam, boiled in 25-30 minutes and heated for an hour. The gap between indicator points is again determined after the system is cooled. The gap should not reach 10 mm in good quality concrete.
Autoclave Test
Cement paste (of ordinary consistency) is put in an autoclave (high-pressure steam vessel) and taken to 2.03 MPa gradually, and then stored for 3 hours there. The improvement in length of the sample is measured and calculated in percentage (after slowly taking the autoclave to room temperature and pressure). The prerequisite for high-quality cement is an autoclave expansion of up to 0.80%.
Standard autoclave test: AASHTO T 107 and ASTM C 151: Autoclave Expansion of Portland Cement.
Consistency of Cement
Cement is the most important material of construction. This plays an important role in obtaining the structure’s strength and durability. It is, therefore, most essential to use the stated generic and good quality cement. General overview and highlights of various cement experiments are already mentioned in our previous article called “Field vs. Cement research laboratory.” The generic reliability analysis of concrete, innovative technique, uses, approval conditions, product quality, test value, etc. will be addressed here.
To deal with cement constituent, i.e. mortar, concrete, etc., they need to apply sufficient water as liquid plays a significant role in the hydration phase. Excess water renders it damp and it’s cool with low water. It is, therefore, most important to maintain the optimal water-cement ratio.
A standard cement consistency test is performed to determine the water content needed to produce a standard consistency cement paste. A flow of a freshly mixed cement paste or mortar refers to consistency as the ability. As a regular consistency or natural reliability, the consistency of cement is also called.
Strength of Cement
Three types of concrete strength–compressive, tensile and flexural–are calculated. Different factors influence capacity, such as water-cement ratio, cement-fine aggregate ratio, healing conditions, size and shape of a sample, moulding and mixing process, loading conditions and age. The following should be considered when evaluating the strength:
- The quality of cement mortar and concrete strength of cement are not directly related. The durability of concrete is simply a function of quality control.
- The toughness checks were carried out on the concrete mortar blend, not on the cement paste. Cement develops strength over time, so it should be listed the precise time it takes to run the experiment.
Compressive strength
Compressive strength and contraction resistance is a substance or structure’s ability to withstand loads that appear to reduce in volume, as compared to tensile strength that can handle loads that continue to elongate. In other terms, compressive strength is immune to pressure (push together), whereas tensile strength is sensitive to stress (pulling apart). Tensile force, compressive strength, and shear strength can be separately measured in the study of surface quality.
Some materials fracture at their compressive strength limit; others irreversibly deform, so that a certain amount of deformation can be considered as the compressive load limit. Compressive strength is a key value in structural design.
Measuring the compressive strength of a steel drum Compressive strength is often measured on a universal testing machine; these range from very small table-top systems to ones with over 53 MN capacity.[1] Measurements of compressive strength are affected by the specific test method and conditions of measurement. In comparison to a specific technical norm, compressive strengths are usually reported.
Tensile strength
Although this experiment used to be common in the early years of cement manufacturing, it does not now provide any useful information regarding cement products.
Flexural strength
In addition, this is a calculation of bending tensile strength. The experiment is carried out in a concrete mortar frame of 40 x40 x 160 mm that is packed at its middle before failure
Setting Time of Cement
When the liquid is applied, concrete sets and hardens. Depending on multiple factors such as cement fineness, cement-water ratio, chemical content, and admixtures, this setting time may vary. Cement used in the building should have an initial setting period not too low and not too high a final setting time. Hence, two setting times are measured:
Initial set: When the paste noticeably starts to stiffen (typically within 30-45 minutes)
Final set: If the cement hardens, it can withstand some load (it happens less than 10 hours)
Heat of Hydration
Hydration heat is the heat generated by the reaction of water and cement from the portland. Hydration energy is most determined by the ratio of C3S and C3A in concrete but is also affected by the ratio of liquid cement, fineness, and temperature heating. Hydration energy decreases as each of these variables rises. Hydration heat is generated significantly faster than it can be dissipated in large-scale concrete structures such as gravity dams (especially in the center of large concrete masses), which can create high temperatures in the center of these large concrete masses that, in effect, can cause undesirable stresses when concrete cools to ambient temperature.
Loss of Ignition
Loss on ignition is a test that is used in inorganic analytical chemistry, particularly in the mineral analysis. This consists of heating a specimen of the product intensely “igniting” at a given temperature, causing unstable compounds to escape before their mass stops increasing. This can be achieved in water or in some other environment that is sensitive or inert. The simple test typically consists of putting a few grams of the substance in a tared, pre-ignited crucible and deciding its weight, positioning it for a set time in a temperature-controlled furnace, cooling it in a regulated environment (e.g., water-free, CO2-free) and re-determining the volume.
The ignition failure is recorded as part of a mineral’s chemical or oxide analysis. Usually, the lost volatile materials consist of “combined water” (hydrates and labile hydroxy-compounds) and carbonate dioxide. It can be used as a quality test, usually done for minerals like iron ore. For eg, the fly ash ignition loss consists of unburnt fuel contaminants.
Bulk density
The liquid covers regions where moisture will usually be present if the concrete was mixed with water. Because of this, cement’s bulk density is not very significant. Concrete has a wide thickness spectrum based on the amount of concrete content. Cement density can be between 62 and 78 pounds per cubic foot anywhere.
Specific Gravity (Relative Density)
Specific gravity is commonly used in the calculation of the sample proportion. Portland cement has a specific gravity of 3.15, but other cement forms (e.g. portland-blast-furnace-slag or portland-pozzolan cement) may have a specific gravity of approximately 2.90.
Chemical Properties of Cement
Calcium, sand and clay (silicon), bauxite (aluminum) or iron ore is the raw materials of concrete manufacture and may include shells, chalk, marl, shale, coal, blast furnace slag, slate. Concrete raw materials ‘ chemical analysis gives insight into the chemical properties of cement.
Tricalcium aluminate (C3A)
High C3A content makes the concrete immune to sulfate. Gypsum lowers C3A hydration, which in the early stages of hydration produces a lot of heat. C3A has no more than a small amount of energy.
Type I cement: contains up to 3.5% SO3 (in cement having more than 8% C3A)
Type II cement: contains up to 3% SO3 (in cement having less than 8% C3A)
Tricalcium silicate (C3S)
C3S induces both accelerated hydration and hardening and is essential for achieving an initial environment of early strength of the concrete.
Dicalcium silicate (C2S)
Unlike tricalcium silicate, which helps to gain early strength, dicalcium silicate in cement helps to gain strength after a week.
Ferrite (C4AF)
Ferrite is an agent of flux. It lowers the raw materials ‘ melting temperature in the kiln from 3,000 ° F to 2,600 ° F. While it hydrates quickly, it does not greatly contribute to the cement’s strength.
Magnesia (MgO)
Portland cement manufacturing process utilizes magnesia in dry production plants as a raw material. Excess magnesia can make the cement toxic and large, but a small amount of it may add strength to the cement. MgO-based cement production also results in lower CO2 emissions. Everything cement is limited to 6% MgO content.
Sulphur trioxide
Sulphur trioxide in excess amount can make cement unsound.
Iron oxide/ Ferric oxide
While giving power and toughness, the color of concrete is primarily responsible for iron oxide and ferric oxide.
Alkalis
The potassium oxide (K2O) and sodium oxide (Na2O) concentrations decide the cement’s alkali content. The cement that incorporates large amounts of alkali may make it difficult to control the cement setting period. High alkaline cement can cause discoloration when used in concrete with calcium chloride. Ground granulated blast furnace slag is not hydraulic on its own in slag-lime concrete but is “disabled” by introducing alkalis. There is an acceptable maximum of 0.60 million of overall alkali material, determined by Na2O + 0.658 K2O formula.
Free lime
Free lime, which is sometimes present in cement, may cause expansion.
Silica fumes
To enhance a number of properties, including compressive strength, abrasion resistance, and bond strength, Silica fume is applied to cement concrete. Although the modification of silica fume prolongs the setting time, it can provide exceptionally high power. Thus, Portland cement comprising 5-20 percent silica fume is commonly developed for high-strength Portland cement projects.
Alumina
Concrete containing high alumina is capable of withstanding frigid temperatures as alumina is resistant to chemicals. It also accelerates the atmosphere but weakens the concrete.