Durability, concrete

Concrete durability can be considered in terms of the following properties ... 

Direct measurement of the effect of aggressive reagents on concrete durability appears to be confined to sea water and sulfate attack, where in both areas it is recognized that the lower the water-cement ratio, the greater will be the resistance to attack and the use of a water-reducing admixture will be obviously helpful. This is confirmed by work carried out in Holland [95] and Japan [84] and a general conclusion is that a reduction in the water- cement ratio from 0.5 to 0.40, would allow a reduction in thickness of cover of the reinforcement by about 50%. 

There are three major reasons for intentionally entraining air into concrete durability, cohesion and density. 

Kilworth, S.R., J. Fallon, Stainless Steels for Reinforcement, Concrete Durability in the Arabian Gulf, 2nd Regional Concrete Conference, Bahrain, 19-21 March 1995. 

In the case of a concrete structure, the presence of steel reinforcements can further complicate the system by causing a local heterogeneity since they constitute in terms of dose rate (driving of the radiolysis) or by the influence of iron ionic species on radiolysis at the interface with the cement paste. Although still not very well-studied, the resulting radiolysis-corrosion coupling (as a function of temperature) is identified as the only aspect which could possibly affect the concrete durability under radiation [1]. 

P- Nixon, C. L. Page, Pore solution chemistry and alkali aggregate reaction in ACI SP-100 Concrete Durability, ). M. Scanlon (Ed.), American Concrete Institute, Vol. 2, 1833-1862, 1987,... 

G. C. Hoff, Durability of fiber reinforcement eonerete in a severe marine environment, Paper presented at Catherine and Bryant Mather International conference on concrete durability, Atlanta, 1987, pp. 997-1041. 

Kropp, J. and Hilsdorf, H.J. (1995). Performance Criteria for Concrete Durability Rilem Report 12. Product of RILEM Technical Committee 116-PCD. Publ E FN Spon London. 

Bamforth, P. (2004). Enhancing Reinforced Concrete Durability. Concrete Society... 

Ravindrarajah, R. and Ong, K. (1987). Corrosion of Steel in Concrete in Relation to Bar Diameter and Cover Thickness. ACI SP-100 Concrete Durability-Katherine and Bryant Mather International Conference. J.M. Scanlon (ed.), American Concrete Institute, 1987, pp 1667-1677. 

In coimection with the requirements for concrete durability cements are divided also according to alkalis content (see Chap. 6). Cements with high and low alkalis content are distinguished and the threshold value is the sum Na20 +0.658K20=0.6. Certainly there are cements with even lower content of alkalis. 

The water permeability of a paste is an important feature because of its decisive role for the resistance of material to the liquid aggressive media. Hence, this is among the most important paste and concrete durability determining factors. The relation between the permeability and diffusion rate and concrete durability, requires to consider more factors that only the porosity and phase composition of the paste primarily the paste-aggregate interface and the properties of this transition zone must considered. 

There is also a shortage of data on the impact of the transition zones both paste-aggregate and paste-reinforcement on concrete properties. The correlation between concrete durability and strength of bond has not been foimd as yet. Mindess et al. [54] propose some methods of paste with aggregate or reinforcement bond strengthening. The silica fume addition can be apphed very easily. 

The glass, opal silica and zeolites are the components of pozzolanas active in the presence of calcium hydroxide. However, pozzolanas contain also a large amount of inert components, to which the crystalline phases, such as quartz, feldspars, dolomite, magnetite, pyroxenes and calcite belong. Pozzolanas can also contain harmful for concrete durability components i.e. organic substances and swelling clays (montmorillonite). 

Brown s most widely known published work is his Microscopical Study of Clinkers (1948) in which 21 different lots of clinkers were microscopically studied at the Portland Cement Association laboratories in order to correlate mineral composition with what Brown termed the degrees of burning in the cement kiln and concrete durability. Although Brown s description and interpretation of what he termed the glass and dark prismatic phase may be questionable in the light of recent research, his work in clinker and concrete microscopy was seminal. Brown contributed significantly to the discussion of clinker phases in a book by Insley and Frechette (1955). 

Heinz, D., and Ludwig, U. (1997) Mechanism of secondary ettringite formation in mortars and concretes subjected to heat treatment, in Concrete Durability, Katherine and Bryant Mather International Conference (ed. J.M. Scanlon), American Concrete Institute SP-100, pp. 189-194. 

George, C M., and Montgomeiy, R.G.J. (1992) Calcium aluminate cement concrete durability and conversion. A fresh look at an old subject. Materiales de Construccion (Madrid) 42 (228), 51-64. 

Thomas, M.D.A. and Folliard, K.J. 2007. Concrete aggregates and the durability of concrete. Durability of Concrete and Cement Composites, Edited by C.L. Page and M.M. Page, Published by Woodhead Publishing Limited and CRC Press, pp. 247-281. 

Full impregnation is usually achieved by pressure. The principal reason for full impregnation is to improve the strength and other mechanical properties of concrete. Durability improvement accompanies this. 

Berke, N. S., Scali, M. J., Regan, J. C., and Shen, D. F., Long-Term Corrosion Resistance of Steel in Silica Fume and/or Fly Ash Containing Concrete, Second Intertiational Conference on Concrete Durability, Montreal, Canada, 1991, ACI, SP-126, pp. 393-422. 

Gruber, K. A., Ramlochan, T., Boddy, A., Hooton, R. D., Thomas, M. D. A. (2001) Increased concrete durability with high-reactivity metakaolin, Cement and... 

Jalali, S., Peyroteo, A., Ferreira, M. (2006), Metakaolin in concrete - beneficial impact on performance parameters (abstract), in Froc. Int. RILEM Workshop on Performance Base Evaluation and Indicators for Concrete Durability. Madrid, p.49. 

Several aggressive substances may enter the material structure as a result of a combination of these processes. A measure of concrete durability was proposed by Hilsdorf (1989) in the form of an air permeability characteristic, which could complete standard strength in material characterization. 

Zhao Y, Du P, Jin W (2010b) Evaluation of the performance of surface treatments on concrete durability. J Zhejiang Univ Sci A 11(5) 349-355. doi 10.1631/jzus.A0900580... 

The addition of microfibrillar cellulose increases the paste thixotropy both with and without plasticizer. Microfibrillar cellulose helps to make a self-compacting concrete more robust. Water bleeding and aggregate settlement are diminished and thus concrete durability properties are increased. Water bleeding is effectively prevented with the finest fibril additives. The aggregate settlement is also drastically decreased with microfibrillar cellulose (20). 

The four clinker minerals mentioned have characteristic properties with regard to rate of heat development and rate of strength development during hydration subsequent concrete durability and colour. Therefore, the useful quahties of Portland cement depend, at least in part, on the quantitative proportions of these clinker minerals in the cement. 

G.C. Hoff, DurabilityofFiber Reinforced Concrete inaSevere Marine Environment , in Concrete Durability, ACI SP-100, American Concrete Institute, Detroit, Ml, 1987, pp. 997-1026. 

Al-Tayyib and Al-Zahrani [78,79] showed that adding 0.2% polypropylene fibres to the concrete effectively enhanced the durability of the concrete skin when exposed to severe marine environments, and improved the concrete durability by retarding the corrosion of the reinforcing steel. 

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