Geopolymeric cement

Portland cement contains limestone as well as additions of aluminosi-licates such as quartz sand, clay or fly ash. To produce geopolymeric cement the limestone is completely substituted by sodium oxide and processed in a low temperature chemical reaction. Sodium oxide is produced from potassium chloride or sodium chloride in a relatively energy intensive process, but the quantities of raw material required are considerably lower than with limestone. The energy used during production is therefore less, and chemical emissions of carbon dioxide are avoided completely. This cement has somewhat lower pH stability than Portland cement, making the use of steel reinforcing more difficult. It has nevertheless been estimated that around 25% of the

Table 6.10 Additives in cement and concrete

Additive

Contents

Accelerators

Calcium chloride, calcium formiate, amorphous aluminium hydroxides, aluminium sulphate, triethanolamine, thiocyanate, sodium and potassium waterglass

Adhesion increasing agents

Silicones, synthetic resins such as polyvinyl acetate, acrylics, epoxy, polyurethane, styrene and butiadiene compounds

Aerating agents

Hydrogen peroxide, aluminium powder, magnesium, zinc, maleic acid-anhydride

Air-entraining agents

Natural resins (colophony etc), fatty acids and oils, lignosulphonates, alkylpolyglycolether, alkyl sulphonates and alkylsulphates (e.g. ethylene ether sulphate, sodium dodecyl sulphate, tetradecyl sulphate, cetyl sulphate, oleoyl sulphate, phenol etoxylates, sulphonated naphthalenes), tensides, plastic pellets

Anti-alkali reactive agents

Lithium- and barium salts, pozzolanas

Anti-corrosion agents

Sulphites, nitrites, benzoates

Anti-freezing agents

Alcohol, glycols, inorganic salts

De-foaming agents

Tributyl phosphate, polydimethyl siloxane, alcohols

Chromate reducers

Iron-sulphate, Tin-sulphate

Expanders

Iron powder, sulphur-aluminate cement

Fungicides

Formaldehyde compounds (tetramethylolacetylene, benzylhemiformal), phenolic compounds (p-chlor-m-cresol), isolthiazolinones (methylchloroisothiazoline, methylisolthiazoline, benzisothiazoline, n-octyl-isothiazoline), copper salts, dieldrin

Grouting aids

Aluminium powder

Permeability reducers

Bentonite clay, lime, fossil meal

Recycling aid for wash water and concrete remains

Phosphonic acids (2-phosphonobutane-1,2,4 tricarboxylic acid (PBTC)), fruit acids (citric acid)

Retarders

Sucrose, Gluconates (sodium gluconate), phosphates (tetrapotassium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate), borates, silicon fluoride, lead and zinc salts, gypsum

Water reducing agents (plasticizers)

Lignosulphonates, polyhyroxy-carboxyl-acids and salts, polyethylene glycol, melamine formaldehyde sulphonates, naphthalene formaldehyde sulphonates, aliphatic amines, sodium silicate, sodium carbonate, polycarboxylates, nonylphenols

Water repellants

Calcium stearate, stearic acid, oleic acid, fats, butyl stearate, wax emulsions, aluminium stearate, bitumen, silicone, synthetic resins

Water retaining admixtures

Starch derivatives, polysaccharides, polyethylene oxides, polyacrylates, silica dust

Source: Deutche Bauchemie, 2005; Kjœr, 1982.

Source: Deutche Bauchemie, 2005; Kjœr, 1982.

Portland cement used in Europe could be replaced by geopolymeric cement (Kram et al., 2001).

Non-hydraulic binders Lime

Lime reacts as a binder with carbon dioxide in the air to form a stable compound.

This reaction is exothermic in the same way as slaking, in that the energy used in firing is now released. It takes a long time for the lime to set, and the process is slower at low temperatures.

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