CEMENT Prepared by M Sohail saleh M Anees M Zahid Ali Sajjad Shukar Abbas Shukar
INTRODUCTION The term "cement" originates from the Latin word "Caementum", which signifies chopped stone. Definition: “Cement is a crystalline compound of calcium silicates and other calcium compounds having hydraulic properties”.
History Lime and clay have been used as cementing material on constructions through many centuries. Romans are commonly given the credit for the development of hydraulic cement, the most significant incorporation of the Roman’s was the use of pozzolan-lime cement by mixing volcanic ash with lime. In 1824 Joseph Aspdin from England invented the Portland cement
WHAT IS CEMENT???? B inding material. Composite material. Material with adhesive and cohesive properties. Hydraulic properties.
RAW MATERIALS Main constituents of cement include: Lime Alumina Iron Laterite These constituents are obtained from following raw materials: Lime stone Clay Shale Gypsum iron ore Slag / Fire Clay DO YOU KNOW ? 1 ton of Portland cement required 1,6 tons of raw materials
Types of Cement 2 types of cement normally used in building industry are as follows: a) Hydraulic Cement b) Nonhydraulic Cement
Hydraulic Cement Cements are considered hydraulic because of their ability to set and harden under or with excess water through the hydration of the cement’s chemical compounds or minerals
Non-hydraulic Cement It cannot harden while in contact with water, as opposed to hydraulic cement. It is created using materials such as non- hydraulic lime and gypsum plasters etc. which has liquid properties. After non- hydraulic cement is utilized in construction, it must be kept dry in order to gain strength and hold the structure.
Commonly used Types of cement 1 Ordinary Portland Cement (OPC) 2 Sulphate Resisting portland Cement (SRPC) 3 Rapid hardening cement 4 White Cement etc.
Ordinary Portland Cement Artificial cement Made by the mixing clinker with gypsum in a 95:5 ratio. Additional, specific properties can be enhanced by altering the cement-making process or the size of the particles and so producing different cements.
White cement specially selected raw materials, usually pure chalk and white clay containing very small quantities of iron oxides and manganese oxides. White cement is frequently chosen by architects for use in coloured concretes that will be exposed, inside or outside buildings, to the public's gaze.
Rapid Hardening Portland Cements The average particle size is smaller they gain strength more quickly than do opc. They generate more heat in the early stages and can be useful in cold weather concreting.
Uses of R.H.C. In pre-fabricated concrete construction. Where formwork is required to be removed early for reuse. Road repair works. In cold weather concrete where the rapid rate of development of strength reduces the vulnerability of concrete to the frost damage.
Sulfate-Resisting Cements SRPC contain’s a high content of iron oxide in order to limit the amount of the mineral phase (C3A) increase its sulfate resistance. SRPC is normally a low alkali cement which benefits concrete in resisting the alkali silica reaction (ASR)
Uses of S.R.C. Concrete to be used in marine condition; Concrete to be used in foundation and basement, where soil is infested with sulphates; Concrete used for fabrication of pipes which are likely to be buried in marshy region or sulphate bearing soils; Concrete to be used in the construction of sewage treatment works.
Physical Properties of Portland Cements Fineness, Soundness Consistency Setting time Strength Heat of hydration
Fineness of Cement Rate of hydration increases with fineness, leads to high strengths and heat generation.. Finer particles will be more completely hydrated. Increasing fineness decreases the amount of bleeding but also requires more water for workability which can result in an increase in dry shrinkage.
Soundness Soundness is the ability of a hardened paste to retain its volume after setting. A cement is said to be unsound if it is subjected to delayed destructive expansion. Unsoundness of cement is due to presence of excessive amount of hard-burned free lime or magnesia
consistency It refers to the relative mobility of a freshly mixed cement paste For normal consistency of cement the maimum amount of water to be added is 30% The plunger of vicatt’s appratus(10mm diameter) shuold penetrate 10mm
Setting, and Hardening - When cement is mixed with sufficient water, it loses its plasticity and slowly forms into a hard rock-type material; this whole process is called setting. - Gypsum retards the setting process - Hot water and calcium chloride used to accelerate the setting process.
Initial setting Time taken by the paste to stiffen to such an extent the vicatt’s needle not penetrate through the paste 25 mm Measured by Vicatt’s apparatust
Final setting Time after which the vicatt’s needle doesn’t sink visibly nad leave impression on paste Measured by Vicatt’s apparatus
Heat of Hydration Cement + H 2 O = Calcium Silicate Hydrate (C-S-H) +Ca (OH) 2 +H 2 O Early age cracking, due to thermal and shrinkage stress. This is a concern about high performance concrete subjected to higher temperatures Most concrete is made with a water to cement mass ratio ranging from 0.45 to 0.65
Water Cement Ratio Water demand can decrease with increasing limestone content. Increase with fineness of cement. The proportions of gypsum, anhydrite. Dependent on the temperature. Soluble sulphate and C3A reactivity changes.
Disadvantages Limits on flexibility deficiency of natural resources Production of CO 2 Increasing temperature of earth
CO 2 emission in cement production Calcination540kg 55% Burning340kg35% Power 90kg10% Total970kg CO 2 / ton OPC For simplicity 1 ton cement 1 ton CO 2 emission
Time Series Plot for Monthly CO 2 in the Atmosphere 1965-2004
Uses Of Portland Cement Main use is in the fabrication of concrete and mortars Modern uses Building (floors, beams, columns, roofing, piles, bricks, mortar, panels, plaster) Transport (roads, pathways, crossings, bridges, viaducts, tunnels, parking, etc.) Water (pipes, drains, canals, dams, tanks, pools.) Civil (piers, docks, retaining walls, silos, warehousing, poles, pylons, fencing) Agriculture (processing, housing, irrigation) fire-proof material
Storage Cement is moisture-sensitive material; if kept dry it will retain its quality indefinitely. When exposed to moisture, cement will set more slowly and will have less strength compared to cement that kept dray. At the time of use cement should be free- flowing and free of lumps.