Mineral admixtures

For special high strength appHcations, ie, up to 69 MPa (10,000 psi), special formulations of Pordand cement concretes have been developed. These ate based on the use of chemical and mineral admixtures. The typical mineral admixtures ate fumed siUca and other po22olanics. The chemical admixtures ate generally chemicals termed supetplastici2ets that allow very low water to cement ratios, ie, between 0.4 and 0.25, and reduce the amount of water needed to provide plasticity or dow to the concrete. PubHc works appHcations take just under 32% of the total Pordand cement market streets and highways represent 68% of this usage, and water and waste account for 23%. 

Modem concretes often incorporate a mixture of chemical and mineral admixtures, each of which may interact with the various constituents of cements and influence cement hydration reactions. The admixture-cement interactions may in fact be viewed as the reaction between two complex chemical systems - the multicomponent, multiphasic inorganic materials in the cement and the organic compounds of multicomponent admixture systems. For example, lignosulfonate water-reducers are intrinsically complex mixtures of chemical compounds derived from the chemical degradation of lignin, while synthetic admixtures such as superplasticizers contain species with a broad distribution of molecular weights, reaction products, or other chemicals added for a specific purpose [125]. The performance of an admixture in concrete is highly dependent on many... 

ASTM 1994. ASTM C618 Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete. ASTM International. World Wide Web Address http// www.astm.org. 

McCarthy, G. J., Solem, J. K., Manz, O. E. Hassett, D. J. 1990. Use of a database of chemical, mineralogical and physical properties of North American fly ash to study the nature of fly ash and its utilization as a mineral admixture in concrete. Materials Research Society Symposium Proceedings, 178, 3-34. 

One of the most significant uses of fly ash is as a mineral admixture in Portland cement concrete. This use alone accounted for over 56 wt% of the fly ash utilized in the USA in 2001 (American Coal Ash Association 2002). Fly ash is particularly well suited to this application because of its... 

Portland cement clinker potential phase composition is presented in Table 4. It could be seen that the C3A content in the clinker was 9.46% which is important for the cement hydration rate and cement sulfate resistance. Common Portland cement is not resistant to the sulfate influence because of the significant C3A content, whose hydrates react with sulfate ions resulting in expansive compounds. Portland cement with the higher resistance to sulfates must have low C3A content. Moderate to high content of mineral alite - C3S (54.72%) is usual for the Serbian cement plants and enables the addition of higher quantities of mineral admixtures without influencing the quality of final cement. 

Chemical composition of the mineral admixture - coal burning fly ash is presented in Table 5. Because of the lower content of Si02 and high content of CaO this fly ash was not so suitable for the cement production. It also has the increased loss on ignition, yet complying with the Yugoslav standard JUS B.C1.018. It also could be seen that the MgO, alkalies, and S03 content were in the limits of the mentioned Yugoslav standard. 

Pozzolanic activity of the used fly ash sample (Table 6), determined by the test with the hydrated lime according to the mentioned standard, is for the P5 pozzolana class which means that it is convenient for the cement production as the mineral admixture [38-41]. 

Costa and Massazza (C44) concluded from a study of natural pozzolanas of varied types that reactivity in mixtures with CH at w/s = 2 and 40 C depends during the first 28 days on the specific surface area and at later ages on the contents of Si02 and AI2O3 in the active constituents. A comparative study of five natural pozzolanas and three low-CaO pfas in pastes with cement showed that the CH contents of the pozzolanic cements were considerably lower than those of the pfa cements at 3-60 days, but virtually the same at 90 days, the pozzolanas thus appearing to react more rapidly than the pfas at early ages but more slowly later. Determinations of the unreacted mineral admixture in pastes with CH showed that at 90 days 23-30% of the natural pozzolana had reacted, compared with 11-15% for the pfas. The similarity in CH contents suggests, however, that these values may not apply to mixtures with cement. 

Water-reducing admixtures and set controlling admixtures Finely divided mineral admixtures Admixtures for no-slump concretes... 

GBFS is used as a mineral admixture for Portland cement concrete... 

Fly ash has been successfully used as a mineral admixture in PCC for nearly 58-65... 

Fly ash must be in a dry form when used as a mineral admixture... 

ASTM (1994) Standard specification for fly ash and raw or calcined natural pozzolan for use as mineral admixture in Portland cement concrete. American Society for Testing and Materials, Annual Book of ASTM Standards, C618-92a, vol 04.02, West Conshohocken, PA, p 194... 

Figure 4.44 shows the water permeability as measured parameter, time (s), by Figg s methodi 1 of dry-cured EVA-modified mortars with blended cements containing various mineral admixtures. According to this method, the measured parameter is the time taken for a standard volume of water to be permeated into the specimen through a 10 nun diameter x 40 mm deep hole.P 1 An increase in the measured parameter of EVA-modified mortars with the blended cements indicates a decrease in the water perme-ability, and increasing polymer-cement ratio decreases the water permeability by a factor of 10 or more. 

In addition to low chloride permeability, mineral admixtures impart other properties to the concrete depending on the admixture selected such as ... 

An FHWA study by Thompson and Lankard (19, 20) reviewed the effect on the corrosion of steel in the concrete of several variables, including cement type, mineral admixtures, water-to-cement ratio, and aggregate type. This study showed silica fume to be the most effective mineral admixture in the mitigation of corrosion of steel rebar. It also suggested that careful selection of the concrete mix components could extend the life of a concrete bridge member. It is estimated that use of a silica fume admixture provides an increase of expected life of 10 years beyond that provided by black steel rebar in conventional concrete. 

I. Turkmena and M. Gavgalib, Influence of mineral admixtures on the some properties and corrosion of steel embedded in sodium sulfate solution of concrete, in Journal of Materials Letters, Vol. 57, 2003, pp. 3222-3233. 

Their physical properties are listed in Table 4. FA and SF were also used as mineral admixtures. The physical properties of each admixture are listed in Table 5 and 6. For the chemical admixtures, polycarboxylate-based superplasticizer and negative ion type AE agent were used. 

Cochet, G., and Sonentino, F. (1993) Limestone filler cement properties and uses, in Mineral Admixtures in Cement and Concrete (ed. S.N.Ghosh), ABI Books, New Delhi, pp. 212-295. 

Rosenberg, A.M., and Gaidis, J.M. (1989) New mineral admixture for high strength concrete. Concrete International Design and Construction 11,31-35. 

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