Home Random Page


CATEGORIES:

BiologyChemistryConstructionCultureEcologyEconomyElectronicsFinanceGeographyHistoryInformaticsLawMathematicsMechanicsMedicineOtherPedagogyPhilosophyPhysicsPolicyPsychologySociologySportTourism






Admixtures for Concrete

( 1400 οεχ. ην. )

 

Concrete can sometimes be improved by an admixture added to the cement, aggregates and water to modify one or more of the properties of the mix. Admixtures are not magic powders that can be added indiscriminately to poor concrete mixes to make good concrete. Neither can it be assumed that they will necessarily make good concrete better. The right admixture for the job must be used if the admixture is to do more good than harm. When a change is made to improve one property of concrete, some other properties will be affected, frequently adversely.

Principal admixtures are: air-entraining agents and water-reducing admixtures. Perhaps the most widely used admixtures are air-entraining agents. Air-entrainment is used to improve the resistance of concrete to damage from freezing and thawing. It also makes concrete slabs much more resistant to scaling where salts are used for deicing. It makes the mix more workable or at least more cohesive. It permits a substantial reduction in the water requirement and consequently the cement content in mass concrete and has helped with the temperature problem by reducing the amount of heat generated during setting of the cement. Air entrainment is generally considered to be the greatest advance in concrete technology in recent years.

Water-Reducing Admixtures

 

Use of water-reducing admixtures has expanded rapidly in the past few years. The name comes from the ability of these additives to reduce the mixing water required. Also they generally increase strength and they may take it possible to meet a strength requirement that could not otherwise be met with the cement and aggregate at hand.

 

 

Corrosion of Concretes

( 3600 οεχ. ην.)

 

Many times we know, that the concretes with a various course of corrosion are otherwise the same. They are produced from the same concrete, on the same producing equipment, by the same people, the concretes had the same treatment, static loadings and they have ( from the statistical point of view ) also the same physical/ mechanical parameters ( of strength ). Obviously it is valid, that we do not dimension the concretes correctly until now against corrosion.

The corrosion loading is not given in the concrete structures first of all by the influences of the environment and is not characterized by the present static solution. The environment is a continually changing resultant of the cumulated effect of various variables. Among them certainly belong the changing temperature and the temperature gradients, aggressive materials and further elements.

We are of the opinion, that the problems of the surface corrosion are rooted in deeper connections. We do not know, if it is possible to use various simplifications of the entrance parameters for further treatment, we do not know the laws of the parallel effect of various influences and decisively it is not possible to consider the concrete structures up to the age of 28 days.

 


Date: 2015-12-17; view: 898


<== previous page | next page ==>
Reinforced Concrete | to your current job?
doclecture.net - lectures - 2014-2024 year. Copyright infringement or personal data (0.007 sec.)