Through years of research and development, AfriSam cement products have been specially engineered to extract maximum value from the use of mineral components. Using our C-Tech technology, our products offer eight distinct advantages over pure cements.
While pure Portland cement has served mankind well for over a century, its high carbon footprint and often relatively inferior performance in many concrete applications compared to composite cements render it a product of bygone times.
As part of our efforts to conserve the environment, AfriSam has perfected the art of producing composite cements using additives such as Fly Ash, Ground Granulated Blast Furnace Slag (GGBFS) and limestone as partial replacement for cement. These products are known to have pozzolanic properties, known to behave like pure cements in the presence of cement or lime. Not only does this practice of re-cycling by-products from other industries minimise harm to our environment, but these additives enhance the performance of cement and offer advantages over Ordinary Portland Cement. Fly Ash is a by-product of coal-powered power stations while GGBFS is from the steel industry.
AfriSam’s knowledge of composite cements and the use of admixtures continues to give us a competitive edge, both technically and commercially. Our range of cement products with C-Tech technology offer our customers guaranteed quality performance and peace of mind.
The 8 Reasons why AfriSam cements are better
- Improved workability to allow for a naturally workable mix using less water
- Reduced heat of hydration to minimise thermal cracking
- Reduced susceptibility to chemical attack to limit attack to steel rebar
- Reduced permeability thereby increasing corrosion resistance to steel rebar
- Increased erosion resistance to minimise the impact of water penetration
- Continues to gain strength over time to create a more durable concrete
- Increased durability from the combined benefits described above
- Low carbon footprint to minimise damage to the environment
1. Improved workability
In its simplest form, concrete is a mixture of water, cement, sand and coarse aggregates. A concrete is described as workable if it can be easily mixed, placed, compacted and finished. A naturally workable mix requires less water for the mix to reach the desired consistency and consequently achieves much higher strength levels. While water content in concrete plays a huge role on the workability, adding more water to the concrete increases workability, yet reduces the ultimate strength achieved and negatively impacts on the durability properties of the hardened concrete. Consequently, concrete technologists are continuously evaluating ways to produce naturally workable concretes that require proportionately less water to achieve the desired workability. Improved workability also results in a superior off-shutter or floated finish.
2. Reduced heat of hydration
When substantial concrete structures are cast, thermal stresses that result from the high temperatures generated as a result of the heat not being able to escape quickly enough can cause severe cracking if not managed appropriately. Composite cements used in concrete of similar long term strength also generate heat, but over longer periods of time. Consequently the peak temperatures and thermal gradients are lower, significantly reducing the likelihood of cracking.
3. Reduced susceptibility to chemical attack
The degree of acceptable permeability is different for different applications and environments. It is generally true to say that the more refined the pore structure of the cementitious paste in the concrete, the less susceptible the concrete will be to ingress of undesirable compounds (For an explanation on pore structure, see the discussion under ‘Improved workability’).
So successful have Portland Fly Ash cement composites been in combating attack by sulphates, that previously manufactured “Sulphate Resistant Portland Cement” has been replaced in most parts of the world by composite cement technology which has a relatively low C3A content.
4. Increased erosion resistance
There are two common problems in products bound together with Portland cement.
Firstly, the by-product of a pure cement:water reaction is lime (calcium hydroxide). Whilst this is beneficially alkaline, it can be rapidly neutralised by carbon dioxide penetrating the pore structure or carried into the pore structure by acidic rainfall.
Secondly, acidic rainfall often contains sulphur in various forms which attack of one of the cements compounds (Tri Calcium Aluminate – C3A) by sulphur bearing carriers which can lead to the rapid deterioration of the concrete as a result of an expansive compound forming within the concrete itself.
Both of these mechanisms weaken the pore structure of the concrete, making it more vulnerable to erosion, be it by direct abrasion or liquid erosion. This is not the case for composite cements.
Using sound aggregates is also an essential consideration if erosion is to be resisted.
5. Reduced permeability thereby increasing corrosion resistance
The degree of acceptable permeability is different for different applications and environments. The finer particles in GGBFS, Fly Ash and limestone give composite cements their reduced permeability properties. It is generally true to say that the more refined the pore structure of the cementitious paste in the concrete, the less susceptible the concrete will be to ingress of undesirable compounds. Reduced permeability also assists with slowing down the carbonation process.
Both Fly Ash and GGBFS have been exhaustively researched with respect to reducing chloride ingress and the containment of ions that promote the passage of electrons necessary for corrosion of steel imbedded in concrete. Consequently these products are frequently specified for inclusion in concrete in coastal and other chemically aggressive environments. The use of these additives in cement has a substantial effect in reducing permeability thereby maintaining the alkalinity of the concrete.
This resistance to water and sulphate penetration from the refined pore structures helps protect the concrete from attack, increasing corrosion resistance and preventing the deterioration of the concrete.
6. Continues to gain strength overtime
AfriSam composite cements with C-Tech contain mineral components which are known to produce superior long term strengths. Tests consistently indicate a continued increase in strength gain over time compared to pure cements where strength gain normally flattens out at about 28 days. The reason for this is that Fly Ash uses the cement: water reaction 'lime” to form additional cementitious compounds that contribute to strength.
Cement and concrete containing GGBFS has a higher ultimate strength than concrete made with Portland cement. This is due to a higher proportion of the strength-enhancing calcium silicate hydrates (CSH) than concrete made with Portland cement and a reduced content of free lime, which does not contribute to concrete strength. Concrete made with GGBFS continues to gain strength over time, and some references even claim a doubling of its 28-day strength over periods of 10 to 12 years. The replacement level of GGBFS can be as high as 70% of cement, which is about twice as much of PFA (typically replacement level is 40%).
7. Increased durability
Durability can be defined in many ways, for many different applications. It is essentially defined by answering the question, ‘will the concrete specified meet the purpose for which it was specified and for the anticipated service period of the structure with an acceptable and predetermined amount of maintenance?’.
In general, durability of concrete is dependent of the strength of the concrete chosen for the mix and the pore structure of that particular mix. All of the factors above combine to make concrete with AfriSam cements more durable.
8. Low carbon footprint
Concrete is the most widely used material on earth, eclipsing the combined volumes of all other man made materials by a factor of ten. In terms of its embedded carbon, it is a benign product associated with relatively little CO₂ per unit mass when compared to other materials such metals, glasses and polymers. Conversely, it is made in such vast quantities that it is responsible for over five per cent of anthropogenic CO₂.
Despite recent advances in kiln design and alternative low energy clinkers, the greatest carbon savings from the industry are likely to be made by the inclusion of mineral components like limestone, GGBFS and PFA.
Choice of materials not only relates to cement blends, but also to other materials such as aggregates and structural components, all of which may have higher or lower carbon footprints. In addition to embodied constructional carbon, it is now widely accepted that the overall footprint of the project includes operating energy consumption and the destination of the materials in the project at the end of its service lifetime. The role of appropriate cementitious materials as enablers for reusing resources and giving low operational carbon designs is being increasingly appreciated in mainstream construction.