AfriSam cement products are specially engineered to extract maximum value from the use of mineral components. Our proprietary C-Tech Composite Technology gives our products eight distinct advantages over pure cements.
While pure Portland cement has served mankind well for well 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 Pulverised Fly Ash (PFA), Ground Granulated Blast Furnace Slag (GGBFS) and limestone as partial replacements for cement. These products are known to have pozzolanic properties and to behave like pure cements in the presence of cement or lime.
Fly Ash is a by-product of the coal-fired power generation industry while GGBFS is from the steel industry. Not only does this practice of recycling 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.
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 offers our customers guaranteed quality performance and peace of mind.
The 8 Reasons why AfriSam C-Tech composite cements are better:
Improved workability allows for a naturally workable mix using less water
Reduced heat of hydration to minimise thermal cracking
Reduced susceptibility to chemical attack on steel rebar
Reduced permeability thereby increasing resistance to corrosion 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
Low carbon footprint which minimises damage to the environment
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.
Less water is needed for a naturally workable mix to reach the desired consistency, which means the concrete has higher strength levels. Adding more water to the concrete increases workability yet reduces the ultimate strength achieved. This negatively impacts 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.
When substantial concrete structures are cast, thermal stresses can result from the high temperatures because the heat cannot escape quickly enough. If not managed correctly, this can cause severe cracking.
Composite cements used in concrete of similar long term strength also generate heat, but over longer periods of time. Therefore the peak temperatures and thermal gradients are lower, significantly reducing the likelihood of cracking.
The degree of acceptable permeability varies based on application and environment. The more refined the pore structure of the cementitious paste in the concrete, the less susceptible the concrete will be to the entrance of undesirable compounds (For an explanation on pore structure, see the discussion under ‘Improved workability’).
Portland Fly Ash cement composites have been so successful at 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.
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 attacks one of the cements compounds (Tri Calcium Aluminate – C3A). Sulphur bearing carriers 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.
Use sound aggregates to resist erosion.
The degree of acceptable permeability varies based on application and environment. The finer particles in GGBFS, Fly Ash and limestone give composite cements their reduced permeability properties. 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 to determine how to reduce chloride ingress and contain ions that promote the passage of electrons necessary for corrosion of steel embedded in concrete. 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.
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. This is because Fly Ash uses the cement:water reacting '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 as PFA (typically replacement level is 40%).
Durability 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 on 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 cement more durable.
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, concrete is a benign product associated with relatively little CO₂ per unit mass when compared to other materials such as metals, glass 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 relates to cement blends as well as other materials such as aggregates and structural components, all of which may have higher or lower carbon footprints. In addition to embodied carbon, 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.