“”1Samadar SalimCE-444 PROPERTIES OF FRESH AND HARDENED CONCRETE
“”2Definition: Concrete having a 28-day compressive strength greaterthan 17 MPa and an airdried unit weight not greater than 1850kg/m³.Composition: Similar to normal concrete except that it is made withlightweight aggregates or combination of lightweight and normal-weight aggregates. All lightweight concretes use both lightweightcoarse and lightweight fine aggregates.Sanded lightweight concretes used natural sand instead oflightweight fine aggregates.Lightweight Concrete
“”3Lightweight aggregates that used in structural lightweight concreteare typically expanded shale, clay or slate materials that have been fired in arotary kiln to develop a porous structure.Other products such as air-cooledblast furnace slag are also used.There are other classes of non-structural LWC with lower density made withother aggregate materials and higher air voids in the cement paste matrix,such as in cellular concrete.
“”41. Lightweight Aggregate CONCRETEPorous lightweight aggregate of low specific gravity is used in this concrete.such as pumice, scoria and most of volcanic origin and the artificial aggregatesuch as expanded blast-furnace slag, vermiculite and clinker aggregateTypes of Lightweight ConcreteThe lightweight aggregate concrete can be divided into two typesaccording to its application :One is partially compacted lightweight aggregate concrete and theother is the structural lightweight aggregate concrete.
“”5compacted lightweight aggregate concrete is mainly used for twopurposes that is for precast concrete blocks or panels and cast in-situ roofsand walls. The main requirement for this type of concrete is that it shouldhave adequate strength and a low density to obtain the best thermalinsulation and a low drying shrinkage to avoid crackingStructural lightweight aggregate concrete is fully compactedsimilar to that of the normal reinforced concrete of dense aggregate.It can be used with steel reinforcement as to have a good bondbetween the steel and the concrete. The concrete should provideadequate protection against the corrosion of the steel
“”6 Foamed Slag – was the first LWA suitable for reinforced concrete.(that was produced in large quantity in (UK) Sintered Pulverised – fuel ash aggregate – is being used in the UK for avariety of structural purposes and is being marketed under the tradename Lytag. Expanded Clays and Shales – capable of achieving sufficiently highstrength for prestressed concrete Pumice – is used for reinforced concrete roof slab, mainly for industrial roofs
“”72) AERATED CONCRETEAerated concrete is a lightweight, cellular material consistingof cement or lime and sand or other silicious material it does not containcoarse aggregate.Two methods to prepare the aerated concrete.The first method is to inject the gas into the mixing during its plasticcondition by means of a chemical reaction.The second method, air is introduced either by mixing-in stable foam orby whipping-in air, using an air-entraining agent.Concrete of this type has the lowest density, thermal conductivity andstrength.Aerated concrete used as a structural material usually of high-pressuresteam-cured. It is thus factory-made and available to the user in precastunits , for floors, walls and roofs. Blocks for laying in mortar or glue aremanufactured without any reinforcement. Larger units are reinforcedwith steel bars to resist damage through transport, handling andsuperimposed loads.
“”93) NO-FINES CONCRETEThe term no-fines concrete generally means concrete composedof cement and a (9-19mm) coarse aggregate only (at least 95 percentshould pass the 20mm BS sieve), and the product so formed has manyuniformly distributed voids throughout its mass.No-fines concrete usually used for both load bearing and non-loadbearing for external walls and partitions.The structure of NFC makes it ideal for use as a drainage layer underreservoir and basement floors. It can also serve as an insulating layer and asa damp-proofing material , is NOT suitable for drainage purposes where thewater is soft or aggressive to concrete.Although the strength of no-fines concrete is considerably lower than thatof normal-weight concrete, and increases as the cement content isincreased
“”11Type OfLightweightConcreteType Of Aggregate Grading of Aggregate (Rangeof Particle Size)Partially compactedlightweightaggregate concreteClinkerFoamed slagExpanded clay,shale,slate,vermiculite and perliteSintered pulverized-fuelashand pumiceMay be of smaller nominal singlesizes of combined coarse andfine (5mm and fines) material toproduce a continues but harshgrading to make a porousconcreteStructurallightweightaggregate concreteFoamed slagExpanded clay, shale orslateand sintered pulverizedContinues grading from either20mm or 14mm down to dust,with an increased fines contentThe differences between the types of light weight concrete are very much relatedto its aggregate grading used in the mixes
“”12No-fines concrete Natural AggregateBlast-furnace slagClinkerNominal single-sized materialbetween 20mm and 10mm BSsieveAerated concrete Natural fine aggregateFine lightweight aggregateRaw pulverized-fuel ashGround slag and burnt shalesThe aggregate are generallyground down to finer powder,passing a 75 m BS sieves, butμsometimes fine aggregate(5mmand fines) is alsoincorporated
“”13LWC can be classifiy :1.Low density concrete ( 0.69 to 6.89N/mm²) Compressive strength2.Moderate strength concrete (6.89 to 17.24N/mm²) Compressive strength3.Structural concrete (17.24N/mm²) Compressive strengthClassification
“”141. LOW DENSITY CONCRETEThese are employing chiefly for insulation purposes. With low unitweight, seldom exceeding 800 kg/m³, heat insulation value arehigh. Compressive strength are low, regarding from about 0.69 to6.89 N/mm².
“”152. MODERATE STRENGTH CONCRETEThe use of these concrete requires a fair degree of compressivestrength, and thus they fall about midway between the structuraland low density concrete. These are sometimes designed as ‘fill’concrete. Compressive strength are approximately 6.89 to 17.24N/mm² and insulation values are intermediate.
“”163. STRUCTURAL CONCRETEConcrete with full structural efficiency contain aggregates which fall onthe other end of the scale and which are generally made withexpanded shale, clay, slates, slag, and fly-ash. Minimum compressivestrength is 17.24 N/mm².Most structural LWC are capable of producing concrete withcompressive strength in excess of 34.47 N/mm². Since the unit weight ofstructural LWC are considerably greater than those of low densityconcrete, insulation efficiency is lower.
“”17 Structural lightweight concrete offers design flexibility andsubstantial cost savings by providing: less dead load, improvedseismic structural response, longer spans, better fire ratings, thinnersections, decreased story height, smaller size structural members,less reinforcing steel, and lower foundation costs Reduction of dead load indicates faster building rates and lowerhaulage and handling costs. Frame structures, considerable savings in cost can be brought byusing LWC for the construction floors, partition and externalcladding.Advantages of Using LWC
“”18 Most building materials such as clay bricks the haulage load is limitednot by volume but by weight. With suitable design containers muchlarger volumes of LWC can haul economically. Important characteristics of LWC is its relatively low thermal conductivity,a property which improves with decreasing density in recent years, Thepoint is illustrated by fact that a 125mm thick solid wall of aeratedconcrete will give thermal insulation about 4 times greater than that of a230mm clay brick wall. Lightweight concrete precast elements offer reduced transportationand placement costs The bond between the aggregate and the matrix is stronger in the caseof LWAC than in normal concrete.
“”19Very Sensitive with water content in the mixture .Difficult to place and finish because of porosityand angularity of the aggregate .In some mixesthe cement mortar may separate the aggregateand float towards the surface.Mixing time is longer than conventional concreteto assure proper mixing . Lightweight Concrete are porous and showspoor resistance to heavy abrasion, replacement oflightweight fines with natural sand improves theabrasion resistance of concrete.Disadvantages of LWC
“”21Definition: Concrete in which heavy aggregate such as magneticand iron are used to increase the density of the concrete andprotection against radiation.HEAVYWEIGHT CONCRETE
“”22 For producing heavyweight concrete uses heavy natural aggregates such as barites or magnetite ormanufactured aggregates such as iron or lead shot. The density achieved will depend on the type of aggregate used.Typically using barites the density will be in the region of 3,500kg/m3,which is 45% greater than that of normal concrete, while withmagnetite the density will be 3,900kg/m3, or 60% greater thannormal concrete. Very heavy concretes can be achieved with ironor lead shot as aggregate, is 5,900kg/m3 and8,900kg/m3 respectively.Barite magnetite lead shotCOMPOSITION
“”23 Except for the heavyweight aggregates and some hydrous ores aswell as boron minerals, the same minerals and proportioningmethods are used for producing heavyweight concrete mixtures asare used for conventional normalweight concrete. For detailspertaining to concrete-making metarials for biological shielding, thestandard specifications should be consulted: ASTM C 637(specification for aggregates for radiation shielding concrete) andASTM C 638(nomenclature of constituents of aggregates forradiation shielding concrete). Because of the high denstiy of aggregate particles, segregation offresh concrete is one of the principal concerns in mix proportioning.From the standpoints of high unit weight and a lower tendency forsegregation, it is desirable that both fine and coarse aggregate beproduced from high-denstiy rocks and mineralsMATERIAL AND MIX PROPORTION
“”24 Due to the rough shape and texture of crushed aggregate particles,heavyweight concrete mixtures tend to be harsh. To overcome thisproblem it is customary to use a finer sand, a greater proportion ofsand in aggregate than conventional concrete, and cementcontents higher than 360 kg/m³.It should be noted that to get around the problem of segregation,sometimes other than conventional methods , such as preplacedaggregate concreting, may be employed. İn this method, afterfilling the forms with compacted aggregate coarser than 6 mm, thevoids in the aggregate are filled by pumping in a grout mixcontaining cement, fine sand, pozzolans, and other pumpabilityaids.
“”25 Heavyweight concrete can be pumped or placed by chutesover short distances only, because of the tendency of coarseaggregate to segregate. Concretes containing borate ores,such as colemanite and borocalcite, may suffer from slowsetting and hardening problems because these minerals aresomewhat solube, and borate solutions are strong retarders ofcement hydration. Unit weights of concrete containing barite,magnetite,or ilmenite aggregate are in the range of 3450 to3760 kg/m³ ; when hydrous and boron ores (which are not ofhigh denstiy) are used as partial replacement for heavyweightaggregate, the unit weight of concrete may come down toabout 3200 to 3450 kg/m³.PROPERTIES OF HEAVYWEIGHT CONCRETE
“”26 Massive shielding walls need not be designed for more than 14 MPacompressive strength; for structural concrete, strengths of the order of 20 to35 MPa are sufficent and not difficult to achieve with the high cementcontents normally used. Strenght is, however, of principal concern in thedesign of heavyweight concrete mixtures suitable for use in prestressedconcrete reactor vessels (PCRV). These are pressure vessels that operate at higher stress levels andtempratures than conventional structures, and concrete is subject toappreciable thermal and moisture gradients. In such cases, inelasticdeformations such as creep and thermal shrinkage should be minimizedbecause they can cause microcracking and loss of prestres. Obviously, theelastic modulus of aggregate and compatibility of coefficients of thermalexpansion between aggregate and cement paste should be considered tominimize microcracking.
“”27 The reactor vessels are usually designed to operate with concretetemperatures up to 71°C, but higher accidental tempratures andsome thermal cycling is expected during the service life.Considerable strength loss can occur when concrete is subjected towide and frequent fluctuations in temperature; hence PCRVconcrete is designed not only for high density but also for highstrength. In a study at the Corps of Engineers, Waterways ExperimentStation, using 430 to 575 kg/m³ Type I portland cement, 12 mm or 38mm maximum magnetite or ilmenite aggregate, and an 0.30 to 0.35water-cement ratio, heavyweight concretes (3680 kg/m³ unitweight) were produced which gave 52 to 65 MPa compressivestrength at 7 days, and 62 to 76 MPa at 28 days.
“”28 The ideal property of normal and high density concrete are high modulus ofelasticity , low thermal expansion , and creep deformation Because of high density of concrete there will be tendency for segregation.To avoid this pre placed aggregate method of concreting is adopted. The high density. Concrete is used in construction of radiation shields. Theyare effective and economic construction material for permanent shieldingpurpose. Most of the aggregate specific gravity is more than 3.5
“”29 They are mainly used in the construction of radiation shields(medical or nuclear power plants). Offshore, heavyweightconcrete is used for ballasting for pipelines and similar structures It is also used for bridge counter-weight and for weighting downunderwater pipelinesUSES OF HEAVYWEIGHT CONCRET