Concrete 1 - Introduction To Concrete

Front 1

What is concrete

Back 1

concrete is a construction material composed of cement (commonly portland cement) as well as other cementitious material such as fly ash and slap cement, aggregate (generally a coarse aggregate such as gravel, limestone or granite plus a fine aggregate such as sand), water, and chemical admixtures.

Front 2

Where does the word concrete come from?

Back 2

Latin word "concretus" which means 'hardened' or 'hard'

Front 3

Durability. what is it? and what are the types of chemical damage?

Back 3

Durability is the ability to withstand wear pressure or damage.concrete will have to resist chemical damage such as alkali - silica reactions, chloride attack and corrosion of reinforcement

Front 4

What is the term used for when wet concrete sets

Back 4

curing! not drying!

Front 5

What is the estimated percent the cement industry produces to global co2 emissions?

Back 5

5%

Front 6

What are the strength properties of concrete? (compressive & tensile)

Back 6

high compressive strength 10-100 N/mm^2low tensile strength 10-15% of compressivesteel reinforcement used to resist tension

Front 7

What does water do? how can the amount of water effect concrete properties

Back 7

water forms cement paste by process of hydration.concrete needs to have a workability, water effects thisLower water content means stronger more durable concretehigher water content means easier flowing concrete and reduced strength

Front 8

Aggregate

Back 8

fine and coarse aggregate make up largest part of concrete (4:2:1)sand, natural gravel and crushed stonerecycled aggregates (crushed demolished 'waste') are increasingly used as partial replacement for natural aggregates

Front 9

Cement

Back 9

portland cement is most common type used in concrete, mortar and plastermixture of oxides of calcium, silicon and aluminiummade by heating limestone (source of calcium) with clay, grinding the product (clinker) with a source of sulphate (usually gypsum)

Front 10

Cement manufacture

Back 10

1A) DRY process: shale (silica & alumina), limestone (calcium) => raw mill => pre heat tower 600°C (CO2 released) => KILN1B) WET process: chalk (calcium), clay (silica & alumina) => washed with water => slurry blending => slurry tank => KILNIMPACTS: quarrying; transportation2) KILN: rotary KILN 1450°C (powered by coal mill, releases water & CO2) => rapid air cool => clinker storage => clinker mill (gypsum added) => silos, bulk transport & bags100-350kg coal to produce 1000kg cementin the KILN lime, silica and alumina become liquid (20-30% recombine) => clinkergypsum controls rate of setting, prevents 'flash setting' of cement

Front 11

cement chemistry - hydration process

Back 11

concrete takes considerable time to gain strength

Front 12

What are the different types of cement?

Back 12

ordinary portland cement, OPCrapid hardening, RHPClow heat portland cementsulphate resisting cement

Front 13

Ordinary portland cement, OPC

Back 13

-most widely used-good as long as there is no exposure to sulphates => sulphate resisting cement is required

Front 14

Rapid hardening, RPHC

Back 14

-achieved by increased fineness. -used to increase speed of construction. -generates too much heat for large structural sections or mass concrete. but can be useful at low temperatures. -only costs slightly more than OPC. -Also has 'ultra high early strength'

Front 15

low-heat portland cement, LHPC

Back 15

-slow hardening-higher ultimate strength. gives the lowest 28 day strength but highest 5 year strength-used for mass concrete e.g. dams

Front 16

sulphate resisting cement, SRC

Back 16

-low tricascium aluminate (C3A) content to avoid sulphate attack, otherwise formation of calcium sulphoaluminate damages concrete due to volume increase.- heat development similar to LHPC-more expensive than OPC

Front 17

name some cement replacement

Back 17

- pulverised fuel/fly ash, PFA: cementitious waste from coal power stations. can be used to partially replace portland cement (up to 60%)- ground granulated blast furnace slag, GGBFS/GGBS: by product of steel production, latent hydraulic properties, replaces up to 80%- silica fume, CSF: silicon industry waste. pure active silica. very fine particles, 0.01-0.5 micrometers. quicker reaction. efficient pore filler. High strength concrete- meta kaolin, MK: calcined China clay. not waste material but more reliable properties. similar to CSF, but CSF is black, whereas MK is bright white. used for 'architectural' concrete

Front 18

name some chemical admixtures

Back 18

accelerators- speed up hydration processretarders- slow down hydration processair entrainments- add tiny air bubbles to reduce freeze thaw damage, increases durability but reduces strength. 1% increase in air = 5% reduction in compressive strengthplasticisers- increases workability, allowing easier placement and less compaction and/or reduce water contentpigments- colour for architectural effectcorrosion inhibitors- used to minimise corrosion of steelwork and reinforcement bars

Front 19

concrete stress - strain behaviour

Back 19

concrete is essentially brittle, fails in brittle fracturemicrocracking occurs between coarse aggregate and hydrated cement paste. cracks are stable up to 30% of ultimate strength.concrete stress strain response is non-linear at higher stresses

Front 20

aggregate

Back 20

aggregate is approximately 75% of concrete (4:2:1)quality and type of aggregate has significant affect on strength stiffness and durability size classification- range of sizes up to a maximum between 10mm and 50mm. typically 20mmsize distribution = gradingtypically two grades: fine (<5mm), coarse (>5mm)shape classification: rounded, irregular, flaky, angular, elongated, flaky and elongatessurface texture: glassy, smooth, granular, rough, crystalline, honeycombed

Front 21

What aggregate makes good concrete

Back 21

sufficiently workable to place with available method of compaction; sufficient strength, stiffness; durablelarge, smooth, rounded aggregate increases workability. but too large can cause problems with reinforcementwell graded aggregatereactive aggregates can result in reduced durabilityaggregates affect surface finish - angular & hard wearing required for road surface or pavementstrength of aggregate is one factor in determining strength of concrete

Front 22

What does the term segregation mean?

Back 22

The downward movement of concrete