Cement process and types

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PensyarahPensyarah

Prof. Madya Dr. Mohammad IsmailProf. Madya Dr. Mohammad Ismail

Fakulti Kejuruteraan AwamFakulti Kejuruteraan AwamUniversiti Teknologi MalaysiaUniversiti Teknologi Malaysia

20092009

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Cement

Aggregate (fine + coarse)

Admixture

Water

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• INTRODUCTION– Common construction material, the properties may

be predetermined by design, selection of constituent materials, and quality control

– The constituent materials of concrete are• cement, aggregates, water and admixtures

– Ingredients mixed → molded → hydration → concrete

CEMENT

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Cement

• Cement is any material that binds or unites – essentially like glue.

• In civil engineering or construction, the word cement or “cementitious material” refer to an ingredient in concrete, mortar or grout

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Cement

Is the product obtained by grinding clinker formed by burning raw-materials (argillaceous and calcareous) primarily consisting of lime (CaO), silicate (SiO2), alumina (Al2O3), and iron oxide (Fe2O3)

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Advantages/ Kebaikan

• Cheap

• Flexibility - (concrete, mortar, grout…)

• Finishes/ Penyudah - versatile

• Compression strength – high

• Protection/ Mengawal - keluli

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Disadvantages

• Low tensile strength/ Brittle (Rapuh)/

• High density/ Berat

• Deteriorate (Boleh rosak) – suceptable to frost/ chemical attack

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Characteristic of cement

• Setting and hardening when mix to a paste with water

• Cohesive and Adhesive

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History of Portland Cement

• 1824 – patented by Joseph Aspdin

• Materials to produce cement were found on the English Isle of Portland

• Thus, called PORTLAND CEMENT

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Cement

• Argillaceous + Calcareous

Silica Lime

Alumina

Ferum oxide

Argillaceous – clay, sandstone, shale

Calcareous – limestone, chalk

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Cement

• Hydraulic cement – able to set and harden under water e.g. OPC, Slag Cement, ggbs

• Non-Hydraulic cement – will not set and harden under water but require air to harden e.g. lime, gypsum

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Manufacturing Process

Two processes:

• Wet Process – softer materials (clay + chalk)

• Dry Process – harder materials (shale + limestone)

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1. Grinding and mixing of raw materials

2. Burning in a rotary kiln

3. Cooling, grinding and sieving

4. Storing, packing and distributing

Steps in manufacturing process

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Manufacturing Process

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Wet Process

1. Materials being ground and mixed with the correct proportions

2. The mixture in a slurry form is fed into a rotary kiln where it is heated/burnt to a temperature of 1500 oC to form clinker

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Wet Process

3. Cooling and grinding – Gypsum (CaSO4) is added during the grinding process to prevent flash setting

4. Storing – stored in silo

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Burning (wet process)

• 100 oC – water is driven off

• 850 oC – limestone changes to calcium oxide and CO2 is liberated

• 1500 oC – CaO reacts with SiO2 to form Calcium Silicate CS

• CaO reacts with other compounds to form Calcium Aluminat (CA) and Calcium Aluminoferit (CAF)

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Dry Process• The process is relatively the same as wet

process except in dry process the raw materials (harder materials) are mixed in dry condition.

• Small amount of water is added to form 12mm in diameter ‘balls’

• The ‘balls’ are burnt in a rotary kiln and the chemical reactions are the same as wet process

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Kursus Forensik Kejuruteraan Pembinaan

Pegawai BPR Malaysia2 Ogos – 7 Oktober 2004

Hotel Seri Malaysia

Johor Bahru

Ordinary Portland Cement (OPC)

Rapid Hardening Portland Cement (RHPC)

Sulphate Resisting Portland Cement (SRPC)

Modified Portland Cement (MPC)

Low Heat Portland Cement (LHPC)

Portland-Blastfurnace Cement (PBC)

Portland-Pozzolan Cement (PPC)

Others

Types of Portland Cement

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Cement differing in chemical composition may exhibit different properties when hydrated

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Ordinary Portland Cement

• By far the most common cement used in general concrete construction when there is no exposure to sulphates in the soil or groundwater

• Minimum fineness of 225 m2/kg

• Rate of hardening is moderate

• Standards; BS 12, MS 522

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Rapid Hardening Portland Cement (RHPC)

• Rapid strength gain due to higher C3S content (70%)

• Minimum fineness of 325 m2/kg• Used when formwork is to be removed early for

reuse or where sufficient strength for further construction is required quickly

• Should not be used in mass concrete construction or in large structural sections because of its higher rate of heat development

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RHPC

• For construction at low temperatures, the use of RHPC may provide a satisfactory safeguard against early frost damage

• The setting time and chemical composition of RHPC and OPC is relatively the same

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Sulphate Resisting Portland Cement

• This cement has low C3A (3.5%) content so as to avoid sulphate attack from outside the concrete

• Minimum fineness of 250 m2/kg• Active salts are magnesium and sodium sulphates

• Sulphate attack is greatly accelerated if accompanied by wetting and drying (splash zone)

• The heat develop by SRPC is not much higher than the low-heat cement, which is an advantage

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Portland-Blastfurnace Cement

• Made by intergrinding or blending Portland cement clinker with granulated blastfurnace slag

• Known as slag cement• Slag contains lime, silica and alumina, but not in

the same proportions as in Portland cement• Minimum fineness of 275 m2/kg• Early strength are generally lower than OPC but

later strength are similar or even higher

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Cont.

• Typical uses are in mass concrete because of low heat of hydration and in seawater construction due to better sulphate resistance

(lower C3A content) than with the OPC

• The amount of slag replacement between 25 to 70% of the mass of the mixture

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Portland-Pozzolan Cement

• Made by intergrinding or blending pozzolans with Portland cement

• A pozzolan is a siliceous or siliceous and aluminous material which itself possesses little or no cementitious value BUT in finely divided form and in the presence of moisture, chemically react with Ca(OH)2 - liberated during the hydration of Portland cement to form compounds possessing cementitious properties

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Cont.

• Portland-Pozzolan cement gain strength slowly and therefore require curing over a comparatively a long period, but the long-term strength is high

• Amount replacement between 25 to 40%

• More durable than OPC

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Compound Chemical formula Abb. Percent

(range)

Rate of reaction

with water

Tricalcium silicate

3CaO.SiO2 C3S 35-65% Medium

Dicalcium silicate

2Cao.SiO2 C2S 15-40% Slow

Tricalcium Aluminate

3CaO.Al2O3 C3A 0-15% Fast

Tetracalcium Aluminoferrite

4CaO.Al2O3.Fe2O3 C4AF 6-20% Medium

Principal Compounds of Portland Cement

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Alkalis in Cement

• Na2O and K2O

• May cause problem – Alkali Silica Reaction

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PROBLEMS

1. What are the three main compounds in the raw materials for the manufacture of cement (limestone or chalk

CaO, Clay or shale Silica SiO2 and Alumina Al2O3)

2. What is the purpose of adding gypsum to cement (add 2-5% gypsum to retard the setting time of cement)

3. What are the four major compounds of portland cement

4. Which is the most reactive compound in portland cement

5. Name a nonhydraulic cement6. Name two hydraulic cement

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