TYPES AND GRADES OF CEMENT DESIGN OF CONCRETE STRUCTURES

WHAT IS CEMENT ? CEMENT IS THE MOST IMPORTANT INGREDIENT AND ACT AS A BINDING MATERIAL, CEMENT HAS ADHESIVE AND COHESIVE PROPERTIES i.e CMENT IS A MATERIAL WHICH POSSESES CEMENTATIOUS PROPERTIES.

HOW CEMENT IS PREPARE ? THERE ARE MANLY THREE PROCESSES OF MANUFACTURING OF CEMENT -: (A) MIXING OF RAW MATERIALS 1. DRY PROCESS OF MIXING RAW MATERIALS 2. WET PROCESS OF MIXING RAW MATERIALS (B) BURNING (C) GRINDING

COMPOUNDS OF CEMENT THE MAJOR COMPOUNDS ALSO KNOWN AS BOGUE COMPOUNDS ARE :- TRICALCIUM SILICATE (C3S) (ALITE) (40-50%) DICALCIUM SILICATE (C2S) (BELITE) (15-30%) TRICALCIUM ALUMINATE (C3A) (CELITE) (8-10%) TETRACALCIUM ALUMINO FERRITE (C4AF) (FELITE) (13-17%)

TYPES OF CEMENT 1.ORDINARY PORTLAND CEMENT (grade 33,43,53) 2.RAPID HARDENING CEMENT 3.LOW HEAT CEMENT 4.BLAST FURNACE SLAG CEMENT 5.AIR-ENTRAINING CEMENT 6.SULPHATE RESISTING CEMENT 7.WHITE AND COLOURED CEMENT 8.HIGH ALUMINA CEMENT 9.PORTLAN POZZOLANA CEMENT 10.OIL-WELL CEMENT 11.MASONRY CEMENT 12.QUICK SETTING CEMENT

ORDINARY PORTLAND CEMENT NEARLY 60% OF THE CEMENT USED IN THE COUNTRY IS ORDINARY PORTLAND CEMENT. IT IS THE MOST SUITABLE FOR USE IN GENERAL CONCERTE CONSTRUCTION WHERE THERE IS NO EXPOSURE TO SULPHATE IN THE SOIL OR IN GROUND WATER. ORDINARY PORTLAND CEMENT HAS A MEDIUM RATE OF STRENGTH DEVELOPMENT AND HEAT GENERATION. THIS TYPE OF CEMENT IS ALSO CALLED NORMAL SETTING CEMENT SINCE ITS SETTING IS NORMAL WHEN MIXED WITH WATER.

RAPID HARDENING CEMENT THE RAPID HARDENING CEMENT IS USED FOR REPAIR AND REHABILITATION WORKS AND WHERE SPEED OF CONSTRUCTION AND EARLY COMPLETION IS REQUIRED DUE TO LIMITATIONS OF TIME, SPACE OR OTHER REASONS. THE CEMENT IS TO BE USED IN COLD WEATHER CONCRETING I.E. 9 TEMP < 5 0C. RAPID HARDENING CEMENT IS BASICALLY OPC BUT ITS FINENESS IS 3250 CM2/GM. AGAINST 2250CM2/GM. IN CASE OF OPC. THE COMPRESSIVE STRENGTH AFTER 1 DAY IS 16 N/MM2 AND THAT OF 3 DAYS 27N/MM2. THESE DAYS HIGHER GRADE OPC ARE AVAILABLE IN THE COUNTRY TO MEET THESE REQUIREMENTS AND THEREFORE, THIS CEMENT IS NOT BEING MANUFACTURED AND MARKETED ON REGULAR BASIS. THE CHARACTERISTICS OF THIS CEMENT CAN BE EFFECTIVELY MET BY ONLY GOOD QUALITY 53 GRADE OPC.

LOW HEAT PORTLAND CEMENT LOW HEAT PORTLAND CEMENT IS PARTICULARLY SUITED FOR MAKING CONCRETE FOR DAMS AND MANY OTHER TYPES OF WATER RETAINING STRUCTURES, BRIDGE ABUTMENTS, MASSIVE RETAINING WALLS, PIERS AND SLABS ETC. IN MASS CONCRETING, THERE IS OFTEN CONSIDERABLE RISE IN TEMPERATURE BECAUSE OF THE HEAT PRODUCED AS THE CEMENT SETS AND HARDENS. THE SHRINKAGE WHICH OCCURS ON SUBSEQUENT COOLING SETS UP TENSILE STRESSES IN THE CONCRETE, MAY RESULT IN CRACKING. THE USE OF LOW HEAT CEMENT IS ADVANTAGEOUS SINCE IT EVOLVES LESS HEAT THAN OPC. THIS CEMENT IS NOT AVAILABLE IN THE MARKET ON REGULAR BASIS AND HAS TO BE OBTAINED ON SPECIFIC ORDERS.

PORTLAND SLAG CEMENT (PSC) IT CONTAINS UP TO 70% GROUND GRANULATED BLAST FURNACE SLAG, WITH THE REST PORTLAND CLINKER AND A LITTLE GYPSUM. ALL COMPOSITIONS PRODUCE HIGH ULTIMATE STRENGTH, BUT AS SLAG CONTENT IS INCREASED, EARLY STRENGTH IS REDUCED, WHILE SULFATE RESISTANCE INCREASES AND HEAT EVOLUTION DIMINISHES. USED AS AN ECONOMIC ALTERNATIVE TO PORTLAND SULFATE-RESISTING AND LOW- HEAT CEMENTS. THE HYDRATION OF SLAG IS INITIATED WHEN LIME LIBERATED IN THE HYDRATION OF PORTLAND CEMENT PROVIDES THE CORRECT ALKALINITY; SUBSEQUENT HYDRATION DOES NOT DEPEND ON LIME. TYPICAL USES ARE IN MASS CONCRETE BECAUSE OF LOWER HEAT OF HYDRATION AND IN SEA-WATER CONSTRUCTION BECAUSE OF A BETTER SULPHATE RESISTANCE (DUE TO A LOWER C3A CONTENT)THAN WITH ORDINARY PORTLAND CEMENT. SLAG WITH A LOW ALKALI CONTENT CAN ALSO BE USED WITH AN AGGREGATE SUSPECTED OF ALKALI REACTIVITY

AIR ENTRAINED CEMENT VINSOL RESIN OR VEGETABLE FATS AND OILS AND FATTY ACIDS ARE GROUND WITH ORDINARY CEMENT. THESE MATERIALS HAVE PROPERTY TO RETRAIN AIR IN THE FORM OF FINE TINY AIR BUBBLES IN CONCRETE. MINUTE VOIDS ARE FORMED WHILE SETTING CEMENT WHICH INCREASES RESISTANCE AGAINST FREEZING AND SCALING ACTION OF SALTS. AIR ENTRAINMENT IMPROVE WORKABILITY AND WATER CEMENT RATIO CAN BE REDUCED WHICH IN TURN REDUCES SHRINKAGE, ETC . AIR ENTRAINED CEMENTS ARE USED FOR THE SAME PURPOSE AS THAT OF OPC.

SRC- SULPHATE RESISTING CEMENT SULPHATE RESISTING PORTLAND CEMENT IS A TYPE OF PORTLAND CEMENT IN WHICH THE AMOUNT OF TRICALCIUM ALUMINATE (C3A) IS RESTRICTED TO LOWER THAN 5% AND 2C3A + C4AF LOWER THAN 25%. THE SRC CAN BE USED FOR STRUCTURAL CONCRETE WHEREVER OPC OR PPC OR SLAG CEMENT ARE USABLE UNDER NORMAL CONDITIONS.  THE USE OF SRC IS PARTICULARLY BENEFICIAL IN SUCH CONDITIONS WHERE THE CONCRETE IS EXPOSED TO THE RISK OF DETERIORATION DUE TO SULPHATE ATTACK, FOR EXAMPLE, IN CONTACT WITH SOILS AND GROUND WATERS CONTAINING EXCESSIVE AMOUNTS OF SULPHATE AS WELL AS FOR CONCRETE IN SEA WATER OR EXPOSED DIRECTLY TO SEA COAST . THE IS 456 (REVISED DRAFT CODE) HAS MADE ELABORATE PROVISIONS FOR USE OF PARTICULAR TYPE OF CEMENT AGAINST DIFFERENT PERCENTAGES OF SOLUBLE SULPHATE SALTS.

WHITE AND COLURED CEMENT IT IS MANUFACTURED FROM PURE WHITE CHALK AND CLY FREE FROM OXIDE. GREYISH COLOUR OF CEMENT IS DUE TO IRON OXIDE. SO, THE IRON OXIDE IS REDUCED AND LIMITED BELOW 1%. COLOURED CEMENTS ARE MADE NY ADDING 5% TO 10% COLOURING PIGMENTS BEFORE GRINDING. THESE CEMENTS HAVE SAME PROPERTIES AS THAT OF ORDINARY PORTLAND CEMENT AND ARE NON- STAINING BECAUSE OF LOW AMOUNT OF SOLUBLE ALKALIS. SODIUM ALUMINO FLUORIDE IS ADDED DURING BURNING WHICH ACTS AS A CAALYSIST IN PLACE OF IRON.

HIGH ALUMINA CEMENT THIS IS NOT TYPE OF PORTLAND CEMENT AND IS MANUFATURED BY FUSING 40% BAUXITE, 40%LIME, 15% IRON OXDE WITH A LITTLE OF FABRIC OXIDE AND SILICA, MAGNESIA, ETC. AT VERY HIGH TEMPRATURE. THE ALUMINA COTENT SHOULD NOT BE LESS THAN 32%. THE RESULTANT PRODUCT IS GROUND FINELY. THE MAIN CEMENT INGREDIENT IS MONOCALCIUM ALUMINATE CA WHICH INTERACTS WITH WATER AND FORMS DICALCIUM OCTAHYDRATE HYDROALUMINATE AND ALUMINIUM OXIDE HYDRATE.

PORTLAND POZZOLANA CEMENT (PPC PORTLAND POZZOLANA CEMENT (PPC) CONTAINS UP TO 35% FLY ASH. THE FLY ASH IS POZZOLANIC, SO THAT ULTIMATE STRENGTH IS MAINTAINED. BECAUSE FLY ASH ADDITION ALLOWS A LOWER CONCRETE WATER CONTENT, EARLY STRENGTH CAN ALSO BE MAINTAINED. WHERE GOOD QUALITY CHEAP FLY ASH IS AVAILABLE, THIS CAN BE AN ECONOMIC ALTERNATIVE TO ORDINARY PORTLAND CEMENT. AS A RULE, PORTLAND POZZOLANA CEMENTS GAIN STRENGTH SLOWLY AND THEREFORE REQUIRE CURING OVER A COMPARATIVELY LONG PERIOD, BUT THE LONG TERM STRENGTH IS HIGH SHOWS THAT SIMILAR BEHAVIOR OCCURS WHERE THE POZZOLANA REPLACES PART OF CEMENT, BUT THE LONG-TERM STRENGTH DEPENDS ON THE LEVEL OF REPLACEMENT.

OIL WELL CEMENT THIS CEMENT IS SO CALLED BECAUSE IT IS MAINLY USED FOR CELLING OIL WELLS. SEALLING OF OIL WELL IS NECESSARY TO PREVENT THE SLIDE OF FRESHLY DRILLED WEL FROM COLLAPSING AND TO KEEP GROUND WATER OUT OF THE WELL SHAFT. OIL WELL CEMENT SHOULD BE CAPABLE OF BEING PUMPED IN THE FORM OF SLURRY FOR ABOUT 3 HOURS WHEN SUBJECTED TO HIGH PRESSURE AND TEMPRATURE. THS CEMENT SHOULD HAVE THE PROPRTY OF SLOW SETTING AND QUICK HARDENING.

MAONRY CEMENT ORDINARY CEMENT, WHEN USED IN MASONRY GIVES A HARSH MORTAR. IT RESULTS IN POOR BOND DUE TO SUCKING OF WATER BY MASONRY. TO AVOID THIS, MASONRY CEMENT CAN BE USED. MASONRY CEMENT IS COMPOSED OF ORDINARY PORTLAND CEMENT CLINKERS, LIMESTONE, GYPSUM AND AN AIR- ENTRAINING AGENT. THESE CONSTITUENTS ARE GROUND TO AN EVEN GREATER FINENESS THAN THAT OF HIGH EARLY STRENGTH CEMENT. THE COMPRESSIVE STRENGTH OF THIS CEMENT IS 17.5 N/MM^2 AT 28 DAYS WHEN STANDARD SAND IS USED.

QUICK SETTING CEMENT THIS CEMENT CONTAINS LESS GYPSUM AND IS FINER THAN ORDINARY PORTLAND CEMENT. THE INITIAL SET STARTS WITHIN 5 MINUTES AND FINAL SET TAKES PLACE WITHIN 30 MINUTES. THE ADDITIONAL OF LESS GYPSUMAND FINE GRINDING ARE RESPONSIBLE FOR ACCELERATING THE SETTING ACTION OF CEMENT. THIS CEMENT IS USEFUL FOR CONCERETE WHICH IS TO BE LAID UNDER STATIC WATER OR IN RUNNNING WATER. THE USE OF QUICK SETTING CEMENT SHOULD BE AVODED IN GENERAL AS IT IS NOT POSSIBLE TO PLAE CONCRETE WITHIN ITS INITIAL SETTING TIME.

GRADES OF CEMENT A. 33 GRADE OPC: IT IS USED FOR NORMAL GRADE OF CONCRETE UP TO M-20, PLASTERING, FLOORING, GROUTING OF CABLE DUCTS IN PSC WORKS ETC. THE FINENESS SHOULD BE BETWEEN 225 AND 280. B. 43 GRADE OPC: IT IS THE MOST WIDELY USED GENERAL PURPOSE CEMENT.  FOR CONCRETE GRADES UNTO M-30, PRECAST ELEMENTS.  FOR MARINE STRUCTURES BUT C3A SHOULD BE BETWEEN 5 - 8%. C. 53 GRADE OPC:  FOR CONCRETE GRADE HIGHER THAN M-30, PSC WORKS, BRIDGE, ROADS, MULTISTORIED BUILDINGS ETC.  FOR USE IN COLD WEATHER CONCRETING.  FOR MARINE STRUCTURES BUT C3A SHOULD BE BETWEEN 5 - 8%

SPECIAL GRADES OF CEMENT (43-S and 53-S): SPECIAL GRADE CEMENT IS MANUFACTURED AS PER SPECIFICATION LAID DOWN BY BIS IS 8112 & 12269. IT IS A VERY FINELY GROUND CEMENT WITH HIGH C3S CONTENT DESIGNED TO DEVELOP HIGH EARLY STRENGTH REQUIRED FOR MANUFACTURE OF CONCRETE SLEEPER FOR INDIAN RAILWAYS. THIS CEMENT CAN ALSO BE USED WITH ADVANTAGE FOR OTHER APPLICATIONS WHERE HIGH STRENGTH CONCRETE IS REQUIRED. THIS CEMENT CAN BE USED FOR PRESTRESSED CONCRETE ELEMENTS, HIGH RISE BUILDINGS, HIGH STRENGTH CONCRETE ETC.

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