Below is listed some common terms in the cement and concrete industry. Beneath each term is some basic technical information regarding this topic. This information is for guidance only and should not be used in any specification type referencing or similar.
Detailed technical information or references on cement and concrete can be obtained from the Cement and Concrete Association of Australia library. This library is one of the best sources of information in this specialized area and is also on the web. For further details email [email protected] ccaa.com.au
Bleed Water Evaporation Formula
(for plastic shrinkage cracking of concrete)
A wide range of adhesives are used in the concrete industry including epoxy resins, acrylics and styrene butadiene rubbers (SBR). Note that polyvinvyl acetates (PVA) should not be used for bonding concrete in wet areas. When adhesives are used to bond old to new concrete, the bonding agent must often still be tacky whilst the new topping is being applied. If the bonding agent is allowed to dry, it can often act as a debonder. Check with the supplier.
There are a whole range of admixtures available in the market place these days. These include Accelerators, Retarders, Water Reducers, Superplastizers (or High Range Water Reducers) and Air Entrainers to name a few. Waterproofers are also admixtures that can be added to the concrete to enhance its ability to repel the ingress of water and the aggressive ions it contains.
Anchoring into concrete refers to discrete structural connections that are integral but separate to the reinforced concrete system. They may be cast-in (with precast operations) or installed later into cured concrete (post-cast) but typically they all present some load-rated embedded steel item in the concrete onto which other elements can be bolted, clipped or clamped either temporarily (eg. for precast handling) or permanently, as part of the main design. There is a variety of mechanical and chemical systems available (also see “Epoxy Resins”), all of which need to be supported by appropriate engineering information to assist design, installation and verification. Concrete anchoring capacity is influenced by concrete strength, anchor proxity to concrete features & other anchors, and the type of anchor considered.
A wide range of cements are available in the marketplace today. These include General Purpose Portland (GP) cements, High Early strength (HE) cements, Low Heat (LH) cements, Sulphate Resisting (SR) cements, Low Shrinkage (LS) cements and Off–White cements. Other mineral additions, pozzolans (or supplementary cementitious cements as they are often referred to) can be added to general purpose cement. These cements are then termed the General Blended (GB) cements.
Prior to 1991 the general purpose cement of the day was called Type A cement. Similarly the high early strength was a Type B cement, the low heat was a Type C cement and the sulphate resisting cement was a Type D cement. Cement manufacturers now are able to blend varying proportions of flyash and/or slag, silica fume and limestone to achieve the required properties of a low heat or sulphate resisting cement.
For overseas visitors who wish to align Australian cements with their American equivalents, a rough guide is: Type I = GP, Type II = GB, Type III = HE, Type IV = LH and Type V = SR.
Coatings are usually applied to provide some form of protection to concrete i.e. abrasion resistance, anti-carbonation, waterproofing, anti-chloride ingress. The coating must be of sufficient thickness and mesh size at micro level to restrict the entry of aggressive molecules. If a coating is too open at micro level then small aggressive molecules e.g. Cl- will penetrate.
Concrete is usually coloured by means of addition of oxides into the mix. Colours such as brown, red and yellow are based on Iron Oxide. Blue and green are usually derived from Cobalt Oxide while White is usually based on Titanium Dioxide.
There are various ways of curing concrete (i.e. keeping the concrete from drying out while it gains strength) including the use of curing compounds. Compounds such as hydrocarbon resins, chlorinated rubbers, wax emulsions and PVA’s are a few on the marketplace at present. They must satisfy the requirements of AS3799-Liquid Membrane Curing Compounds
These chemicals are the most common of the repair materials (particularly for crack repair) and also have wide application in chemical anchoring. Whilst not particularly good at resisting UV (thus a yellowing with time), their bond qualities and structural strength are exceptional. Where small thickness cracks need repair then low viscosity epoxy resins are recommended.
These fibres come in a range of shapes and sizes. They are primarily polypropylene or nylon. The main advantage to using synthethic fibres comes in their ability to hold or intermesh freshly laid concrete together whilst it is still vulnerable to plastic shrinkage cracking. Once the concrete has hardened, the strength of the concrete is a function of its own unreinforced properties and of any other steel reinforcing that may have been included.
These fibres come in an even greater range of shapes and sizes. Their primary function is to provide the concrete with an improved flexural tensile strength. This is why they suit areas such as roundabouts, industrial floors, pools etc where the concrete is subject to flexing and tension. They do not cause concrete to spall when they rust as their cross section is very small and thus the volumetric expansion forces due to rusting are limited.
Floor coatings include polyurethanes, acrylics and other various polymer modified compounds. Self levelling compounds are also quite a popular floor coating as they are easy to apply, can be applied in thin layers if required and can provide a good finish. Slip resistance, ease of cleaning, abrasion resistance are some of the issues that should be addressed
All formwork must satisfy the requirements of AS3610. Timber and steel are the main formwork materials. Formwork should always be stored correctly on site and should be maintained. Correct sizing of formwork is crucial as it is a structural material subjected to structural loads. Variables such as cement typed used, rate of pour, temperature, size of containment all affect the pressure of the concrete against the forms.
There are various classifications for grouts in the marketplace including Type A, B, C, D and Z. Type A is for void filling, B for underpinning, C for machine bases and structural steel (though Type Z has started to satisfy this area), D is now almost non existent, Z is similar to C but has a longer life. Grouts can also be made merely with sand and cement using correct proportioning of cement, sand and water.
Joints are usually provided to control the location of cracking in concrete due to shrinkage. They also provide opportunities for finishing work correctly i.e. with a proper construction joint. If the joint are not formed or located correctly then unsightly random cracking will occur. The quantity of steel required to control shrinkage cracking in slabs and walls can be found in the Concrete Structures Code AS3600 Section 9.4 and Section 11.6.
As outlined in coloured pigments above, oxides are primarily used for colouring concrete. This can done by adding the oxide to the concrete or by merely applying it over the surface of the concrete once bleeding has ceased and then working it into the surface. If it is to be added to the concrete then the usual proportions range anywhere between 1% and 10% of oxide for every kg of cement. Example: if concrete contains 300kg of cement/m3 and you wish to use 5% oxide then you will need to add 15kg of the coloured oxide into the mix.
From a concrete point of view, the most important feature a paint must have is its ability to adhere to the surface. Often paints peel away from the substrate due to i) lack of surface preparation, ii) painting the surface too early (the surface needs to oxidize and thus lower its pH thus providing a less alkaline area), iii) having water penetrate through the concrete and thus bubbling the paint off. Resistance to UV, flexibility and colour control are also crucial.
Polymers are long chain molecules of carbon, hydrogen, oxygen and various other elements. Their advantage is that when added to cement or concrete, they provide it with greater elasticity, flexibility, durability and strength. The term ‘polymer modified concrete’ is becoming more common especially in the repair and protection of concrete industry.
The term precast gives an indication of the method of manufacture i.e concrete cast prior to transporting and erection –most times in a yard away from the actual site where the panel are to be used. This is quite different to Tilt Up panel construction. Attention to quality control in a precast yard is also often easier. Besides architectural panels, precast units include hollow core prestressed panels and structural units such as T beams and box culverts.
As outlined above under Polymers, the more common repair materials are polymer modified concretes. Repairs can also be carried out using straight cement, sand and water however shrinkage can be a problem. Some key parameters one should consider when choosing a repair material are (i) ease of mixing and applying, (ii) resistance to UV, (iii) stiffness of repair material to substrate (iv) surface condition of substrate (v) proximity to ocean.
A sealer must partially penetrate the surface yet provide a form of thin coating over the surface i.e. partly between a penetrant and a coating. Often sealers are chosen to keep out water, carbon dioxide, chlorides and other aggressive compounds. In the case of floor sealers they must also withstand traffic wear. Sealers include acrylics, epoxies, methacrylates and chlorinated rubbers.
Sprayed concrete has terms such as shotcreting and guniting. The two last terms are quite similar however it is believed that guniting is more the spraying of concrete with an aggregate size less than 10mm. Shotcreting is very common in pool construction and other concrete wall and embankment type applications. Important parameters to note are (i) Rebound must not be too great (ii) Reinforcing bars must not shadow other bars else impact will be reduced (iii) Mix must not be too wet (iv) Pressure in line must be adequate
Computer programs have sped up the process of structural design immensely over the past 20 years. Programs now allow the user to design concrete columns without the need for interaction graphs, to design complex slabs with knowing Yield Line Theory, and to analyze multitudes of load combinations in seconds and then produce detailed drawings. More information on programs available in the marketplace can be found under ‘Products Guide’
Steel reinforcement comes in a variety of shapes, sizes (and shortly grades). Steel bars, mesh or fabric, trench mesh, steel fibres, prestressing strand all are made from steel. The higher grade steels that have existed since the mid 80’s have been the 400 MPa and 450 MPa grades. From 2000 onwards these will slowly be replaced with 500 MPa steels (to align ourselves with the direction taken by many countries overseas). Stainless steel whilst more expensive does offer a greater protection especially where the concrete is in an aggressive environment.
Synthetic Polymer Fibres
Macro Synthetic Fibres or sometimes referred to as Structural Synthetic Fibres have been widely accepted as suitable replacement for steel fibres and temperature and shrinkage crack control mesh (WWF). The choice of the correct synthetic fibre is important. BS EN 14889-2 (2006) and Eurocode is just one of the recognised standards that will guide designers in their selection of reliable and conforming products. The fibre supplier will be able to provide CE certification and ISO 9001 certification to demonstrate compliance with this standard.
Macro –Synthetic Fibres shall have a minimum tensile strength of 550MPa and an Elastic Modulus of 10GPa when tested in accordance with the requirements of EN14889-2 (2006).
The performance of the Fibre Reinforced Concrete can be measured in ASTM C1609 beam test. Whilst the addition of macro synthetic fibres will not have any measurable effect on the strength (Mpa), however the addition of any material to concrete will require the mix design to be assessed.
A vast range of waterproofing agents is available in the marketplace today. Some react with the calcium hydroxides in the concrete to form a dense matrix and thus waterproofness, while others line the concrete pores with hydrophobic (water repelling) material. It is advised to contact the suppliers listed on this website for more technical information in this specialized area. A higher grade of concrete (> 32 MPa) will also provide watertightness.