Presentation on theme: "Civil Engineering Materials"— Presentation transcript:
1Civil Engineering Materials Department of Civil, Structural and Environmental EngineeringTrinity College DublinDr. Roger P. West (TCD)And Mr. Peter Flynn (Arup)
2Schedule Lectures: Tutorials: Concrete Laboratory: Weeks 1-3(Wed 3-5): Timber, aluminium, glass and pre-castWeeks 4-9(Mon 10-11, Fri 3-4): Concrete, reinforced concrete and pre-stressed concreteTutorials:Alternate weeks, weeks 4-9, Thursday 5-6pm, commencing Groups 1-20 in week 4 of term, in Joly TheatreConcrete Laboratory:Each laboratory group on either Monday or Thursday, for one week only, as per timetable
4What is Concrete?Concrete is the most widely used construction material in the worldConcrete is a construction material composed of crushed rock or gravel and sand bound together with a hardened paste of cement and water.
19Alternative Cement Replacement Materials Blastfurnace Slag Cement (GGBS)Pulverised-fuel Ash Cement (PFA)MetakaolinRice Husk AshSilica FumeCements in Europe are classed as CEM1 (OPC or RHPC), CEM2-4 (OPC with limestone, PFA or GGBS) in varying proportions pre-blended
20Section A.1 Basic Materials 1. CementChemistry of OPC
23Section A.1 Basic Materials 1. CementSulphate Resistant Portland CementLow triacalcium aluminate content (C3A)Achieved by adding Iron oxide to decrease aluminate proportionsResistant to sulphates but not resistant to strong acidsReduced early heat
24Section A.1 Basic Materials 1. CementPulverised-fuel ash cements (latent hydraulic binder)From burning pulverised coal in power station furnacesReacts with calcium hydroxide (lime) to from cementitious materialResistant to sulphates but not resistant to strong acidsReduced early heat of hydrationReduced early age strength
25Section A.1 Basic Materials 1. CementBlastfurnace Slag Cements (latent hydraulic binder)By-product of iron smelting, quenched slag forms granuelsGenerally blended with OPC up to 35%Reduced early age strengthReduced early heat of hydration
29Section A.1 Basic Materials 1. CementDelivery & StorageUsually packaged in 25kg bags or transported in bulk tankersRetail price €5“Warehouse set”
30Section A.1 Basic Materials 2. WaterShould be free from impuritiesUnsuitable if it contains - sugars- sulphates- chloridesSea water must not be used for reinforced concrete
31Section A.1 Basic Materials HydrationSetting and hardening results from a chemical reaction between the cement and the water, not from a drying process.The reaction is exothermic and is irreversible. The heat produced is known as the “Heat of Hydration” C3A and C3S are the compounds primarily responsible.The paste is usually workable up to two hours before it begins to hardenStrength gain is initially rapid becoming progressively less rapidStrength gain continues indefinitely provided moisture is present. “Curing”
34Section A.1 Basic Materials 2. Cement paste strength gain
35Section A.1 Basic Materials 3. AggregatesGravels, crushed rock and sands that are mixed with cement and water to produce concrete.Coarse aggregates are those that do not pass through a 5mm sieve.Fine aggregates are those that pass through a 5mm sieve.Generally make from 50% to 80% of the concrete mix.Used to reduce cost and modify and imporve properties like strength and drying shrinkage.
36Section A.1 Basic Materials 3. AggregatesQuality RequirementsDurability - Hard- Adequate Strength- No deletrious materialCleanliness - free from chemical impurities- free from organic material- free from dust- excessive washing is not the answer- avoid silica acid aggregates.
37Section A.1 Basic Materials 3. AggregatesAggregate TypesNormal density - Most gravels and crushed rock- Divided into coarse and fineLightweight - Weak porous solids- Good thermal propertiesHigh Density - radioactive screening
39Section A.1 Basic Materials 4. AdmixturesAdditives to the concrete mix to improve certain propertiesMust be used with care as excessive amounts can have adverse effects on the concrete
40Section A.1 Basic Materials 4. AdmixturesAcceleratorsIncreases the rate of strength gain at an early ageMost common is calcium chloride (CaCl) but may corrode steelMost common is calcium chloride (CaCl) but may corrode steelDoes not increase final strength
41Section A.1 Basic Materials 4. AdmixturesWater Reducing Admixtures (Plasticisers)Reduces the amount of water required for a given workabilityMost common is calcium ligno-sulphateReduces the risk of evaporation cracksAir Entraining AdmixturesGenerates evenly dispersed air bubbles in the mixImproves durability against frost and marine environmentsVolume or air entrainment should not exceed 13% of cement paste
42Section A.1 Basic Materials 4. AdmixturesRetarding AgentsReduces the rate of evolution of heatNecessary for very large concrete poursWater-repelling admixturesCan improve impermeability of concrete in basements and water retaining structuresNo substitute for sound concrete
44Section A.1 Basic Materials AdmixturesFoaming AgentsProduces highly flowing light concreteSuperplasticiserProduces flowing normal concrete with high strengthSelf-compactingAllows highly flowing cohesive mix with no need for vibration. It can also be self-levelling.