CVL 2407 Faculty of Applied Engineering and Urban Planning Civil Engineering Department Dr. Eng. Mustafa Maher Al-tayeb 2nd Semester 2013/2014 CVL 2407

Low heat Portland cement The rise in temperature in the interior of a large concrete mass due to the heat development by the hydration of cement coupled with a low thermal conductivity of concrete can lead to serious cracking. Cement having such a low rate of heat development was first produced for use in large gravity dams in the United States and is known as low heat Portland cement (type IV).

Low heat Portland cement The limits of lime content of low heat Portland cement. After correction for the lime combined with SO3 are:

Low heat Portland cement The rather lower content of the more rapidly hydrating compounds C3S and C3A results in a slower development of strength of low heat cement as compared to the ordinary Portland cement, but the ultimate strength is unaffected. In any case to ensure a sufficient rate of gain of strength the specific surface of the cement must be not less than 320 m2/kg

Modified cement (Type II) In some applications, a very low early strength may be a disadvantage, and for this reason a so-called modified (Type II) cement was developed in the United State. This modified cement successfully combines a some what higher rate of heat development than that of low heat cement with a rate of gain of strength similar to that of ordinary Portland cement. Modified cement is recommended for structures where moderately low heat generations desirable or where sulfate attack may occur.

Sulfate - resisting cement In discussing the reactions of hydration of cement, and in particular the setting process, mention was made of the reaction between C3A and gypsum (CaSO4.2H2O) and of the consequent formation of calcium sulfoaluminat. In hardened cement, calcium aluminate hydrate can react with a sulfate salt from outside the concrete in a similar manner: the product of addition is calcium sulfoaluminat forming within the framework of the hydrated cement paste because the increase in the volume of the solid phase is 227 percent gradual disintegration of concrete results.

Sulfate - resisting cement A second type of reaction is that of base exchange between calcium hydroxide and the sulfate resulting in the formation of gypsum with an increase in the volume of the solid phase of 124 percent. These reactions are known as sulfate attack. The salts particularly active are magnesium sulfate and sodium sulfate. Sulfate attack is greatly accelerated if accompanied by alternating wetting and drying.

Sulfate - resisting cement The remedy lies in the use of cement with a low C3A content, and such cement is known as sulfate-resisting Portland cement. The British Standard for this cement stipulates a maximum C3A content of 3.5 percent. The SO3 content is limited to 2.5 percent. In the United State, sulfate-resisting cement is known as Type V cement and is covered by ASTM C 150-94.This specification limits the C3A content to 5 percent, and also restricts the sum of the content of C4AF plus twice the C3A content to 25 percent. The magnesia content is limited to 6 percent.

Sulfate - resisting cement As it is often not feasible to reduce the Al2O3 content of the raw material, Fe2O3 may be added to the mix so that the C4AF content increases at the expense of C3A. The low C3A content and comparatively low C4AF content of sulfate-resisting cement mean that it has a high silicate content and this gives the cement a high strength but, because C2S represents a high proportion of the silicates, the early strength is low. The heat developed by sulfate-resisting cement is not much higher than that of low heat cement.

Sulfate - resisting cement It could therefore be argued that sulfate-resisting cements theoretically an ideal cement but, because of the special requirements for the composition of the raw materials used in its manufacture, sulfate-resisting cement cannot be generally and cheaply made. It should be noted that the use of sulfate-resisting cement may be disadvantageous when there is a risk of the presence of chloride ions in the concrete containing steel reinforcement. The reason for this is that C3A binds chloride ions, forming calcium chloroaluminate. In consequence these ions are not available for initiation of corrosion of the steel.

White cement and pigments For architectural purposes, white concrete or a Pastel color is sometimes required. To achieve best results it is advisable to use white cement with of course a suitable fine aggregate and, if the surface is to be treated also an appropriate coarse aggregate. White cement has also the advantage that it is not liable to cause staining because it has a low content o f soluble alkalis.

White cement and pigments White Portland cement is made from raw materials containing very little iron oxide (less than 0.3 percent by mass of clinker) and manganese oxide. China clay is generally used, together with chalk or limestone free from specified impurities. Oil or gas is used as fuel for the kiln in order to avoid contamination by coal ash. Since iron acts as a flux in clinkering its absence necessitates higher kiln temperatures ( up to 1650'C) but sometimes cryolite (sodium aluminum fluoride) is added as a flux.

White cement and pigments To obtain good color white concrete of rich-mix proportions is generally used the water/cement ratio being not higher than about 0.4.

White cement and pigments Atypical compound composition of white Portland cement is given in Table but the C3S and C2S contents may vary widely. White cement has a slightly lower specific gravity than ordinary Portland cement generally between 3.05 and 3.10. Because the brightness of the white color is increased by a higher fineness of cement, it is usually ground to a fineness of 400 to 450 m2/kg. The strength of whit of Portland cement is usually somewhat lower than that of ordinary Portland cement.

White cement and pigments When a pastel color is required white concrete can be used as a base for painting. Alternatively pigments can be added to the mixer; those are powders of fineness similar to or higher than, that of cement. A wide range of colors is available for example iron oxides can produce yellow, red, brown and black colors chromic oxide produces green color, and titanium dioxide produces white color. It is essential that the pigments do not affect adversely the development of strength of the cement or affect air entrainment.

White cement and pigments For instance carbon black, which is extremely fine, increases the water demand and reduces the air content of the mix. For this reason, some pigments are marketed in the United States with an interground air-entraining agent it is, of course essential to be aware of this at the mix proportioning stage.

Portland bIast furnace cement Cements of this name consist of an intimate mixture of Portland cement and ground granulated blast furnace slag. This slag is a waste product in the manufacture of pig iron, about 300 kg of slag being produced for each ton of pig iron. Chemically, slag is a mixture of lime, silica, and alumina, that is, the same oxides that make up Portland cement but not in the same proportions.

Portland bIastfurnace cement Blast furnace slag varies greatly in composition and physical structure depending on the processes used and on the method of cooling of the slag. For use in the manufacture of blast furnace cement the slag has to be quenched so that it solidifies as glass crystallization being largely prevented. This rapid cooling by water results also in fragmentation of the material into a granulated form.

Portland bIastfurnace cement Slag can make a cementations material in different ways. It can be used together with limestone as a raw material for the conventional manufacture of Portland cement in the dry process. Clinker made from these materials is often used (together with slag) in the manufacture of Portland blast furnace cement. This use of slag, which need not be in glass form, is economically advantageous because lime is present as CaO so that the energy to achieve carbonation is not required.

Supersulfated cement Super sulfated cement is made by grinding a mixture of 80 to 85 percent of granulated blast furnace slag with 10 to 15 percent of calcium sulfate(in the form of burnt gypsum) and up to 5 percent of Portland cement clinker. A fineness of 400 to 500 m2/kg is usual. The cement has to be stored under very dry conditions as otherwise it deteriorates rapidly. Super sulfated cement is highly resistant to sea water and can withstand the highest concentrations of sulfates normally found in soil or ground water, and is also resistant to acids and to oils.

Supersulfated cement Concrete with a water/cement ratio not greater than 0.45 has been found not to deteriorate in contact with weak solutions of mineral acids of pH down to 3.5. For these reasons super sulfated cement is used in the construction of sewers and in contaminated ground although it has been suggested that this cement is less resistant than sulfate-resisting Portland cement. The heat of hydration of super sulfated cement is low.

Pozzolanas One of the common materials classified as cementitious in this book (although in reality only in latent form) is pozzolana which is a natural or artificial material containing silica in a reactive form. A more formal definition of ASTM 618-94 describes pozzolana as a siliceous or siliceous and aluminous material which in itself possess little or no cementitious value but will in finely divided form and in the presence of moisture chemically react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties.

Supersulfated cement The main artificial pozzolanic material, fly ash. The natural pozzolanic materials most commonly are: volcanic ash- the original pozzolana - shales and cherts, and burnt clay. Some natural pozzolana may create problems because of their physical properties; e.g. diatomaceous earth, because of angular and porous form requires a high water content. Rice husks are a natural waste product and there is interest in using this material in concrete

Silica fume Silica fume is a recent arrival among cementnous materials. It was originally introduced as a pozzolana. However, its action in concrete is not only that of a very reactive pozzolana but is also beneficial in other respects. It can be added that silica fume is expensive. Silica fume is also referred to as misosilica or condensed silica fume, but the term 'silica fume' has become generally accepted. It is a by-product of the manufacture of silicon and ferrosilicon alloys from high-purity quartz and coal in a submerged-arc electric furnace.