Unit 1 | unit 1 cement

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Unit - 1

Cement

Q1) What is chemistry of cement?

A1)

Chemistry of Cement

Cement chemistry can have an effect on the dispersion performance of superplasticizers in numerous ways. One of those is thru the ionic composition of the aqueous section and particularly via the quantity of soluble sulfates.
The milestone paper in this problem comes from Yamada and Hanehara (2001).
As defined at the reversibility of polymer adsorption, they made opportunity additions of CaSO4 and Na2SO4 that changed the soluble sulfate concentration and the go with the drift spread, in addition to the adsorption.
The essential step on this paper turned into to devise the relative go with the drift immediately with recognize to the polymer adsorption. This emphasizes the reversible nature of the polymer adsorption already mentioned above.

https://ars.els-cdn.com/content/image/3-s2.0-B9780857090287500078-f07-38-9780857090287.gif

Fig: Chemistry of cement

Q2) What are the main constituents of cement?

A2)

Main constituents of cement

Portland cement is made of 4 essential compounds: tricalcium silicate (3CaO · SiO2), dicalcium silicate (2CaO · SiO2), tricalcium aluminate (3CaO · Al2O3), and a tetra-calcium aluminoferrite (4CaO · Al2O3Fe2O3).
In an abbreviated notation differing from the regular atomic symbols, those compounds are special as C3S, C2S, C3A, and C4AF, wherein C stands for calcium oxide (lime), S for silica, A for alumina, and F for iron oxide. Small quantities of uncombined lime and magnesia are also present, in conjunction with alkalies and minor quantities of different elements.

Q3) What is hydration of cement?

A3)

Hydration of cement

The maximum vital hydraulic elements are the calcium silicates, C2S and C3S. Upon blending with water, the calcium silicates react with water molecules to shape calcium silicate hydrate (3CaO · 2SiO2 · 3H2O) and calcium hydroxide (Ca[OH]2).
These compounds are given the shorthand notations C–S–H (represented with the aid of using the common components C3S2H3) and CH, and the hydration response may be crudely represented with the aid of using the subsequent reactions:

2C3S + 6H = C3S2H3 + 3CH

2C2S + 4H = C3S2H3 + CH

During the preliminary degree of hydration, the discern compounds dissolve, and the dissolution in their chemical bonds generates a large quantity of heat. Then, for motives that aren't absolutely understood, hydration involves a stop. This quiescent, or dormant, length is extraordinarily critical withinside the placement of concrete. Without a dormant length there could be no cement trucks; pouring could should be accomplished right now upon mixing.
Following the dormant period (that can remaining numerous hours), the cement starts to harden, as CH and C–S–H are produced. This is the cementitious cloth that binds cement and urban together. As hydration proceeds, water and cement are constantly consumed.
Fortunately, the C–S–H and CH merchandise occupy nearly the identical extent because the authentic cement and water; extent is about conserved, and shrinkage is manageable.
Although the formulation above deal with C–S–H as a selected stoichiometry, with the method C3S2H3, it does by no means shape an ordered shape of uniform composition. C–S–H is virtually an amorphous gel with a noticeably variable stoichiometry. The ratio of C to S, for example, can variety from 1:1 to 2:1, relying on blend layout and curing conditions.

Q4) Define water requirement.

A4)

Water required

Calculate quantity of water in litre required for one bag of cement, as density of water is ready 1kg/ litre, so 20kg water = 20 litres and 30kg water = 30 litres, as a result you may want 20 to 30 litres of water in step with 50kg bag of cement. Regarding this, “how tons water required for 1 bag of cement?”, one 50kg bag of cement would require 20 to 30 litres of water, whilst one 25kg bag would require 10 to fifteen litres of water, a 20kg bag would require eight to twelve litres of water, one 40kg bag would require sixteen to 24 litres of water or a 94lb bag of Portland cement would require 4.five to 7 gallons of water.
Regarding this, “how a whole lot water do I want for a 50kg bag of cement?”, its rely upon water cement ratio and form of grade of concrete, however commonly you'll want 20 to 30 litres of water blend with one 50kg bag of cement together with 2.five cubic toes of sand and 3.seventy five cubic toes of aggregate. This amount of water can be little extrade in keeping with climate circumstance or temperature.

Q5) Define physical properties and testing of cement

A5)

Cement is one of the maximum famous constructing fabric. It is used as a binder withinside the creation enterprise. It has each adhesion and brotherly love properties. It can bind debris right into a compact long lasting stable mass.
Cement has a huge software withinside the creation enterprise along with: When cement is blended with sand and water to shape a paste, it's miles termed as mortar.
The mortar is used to enroll in bricks or stones and in completing works along with plastering and pointing. When cement is blended with gravel (or beaten stones), sand and water, the composite product is known as concrete. The concrete is the second one maximum used fabric in this planet. It is used for building footings, beams, columns, slabs, stairs, etc. There are many kinds of cement which might be used as in keeping with their necessities and properties
Fineness of Cement

The fineness of cement is the degree of the particle length of cement. The finer the cement, extra is the charge of a chemical reaction. This outcomes in a extra charge of electricity development. Very first-class cement is likewise undesirable. It generates extra warmness which leads to cracks in mortar or concrete. It also can result in a untimely setting.’

Soundness of Cement

The phenomenon of cement to go through unwanted enlargement is called as unsoundness. When the cement does now no longer go through a huge alternate in volume, it will likely be known as sound cement. The unsound cement will fall apart because of volumetric adjustments as a result of the presence of unfastened lime and magnesia in cement. Unsound cement includes a few unfastened lime even after the very last grinding. This unfastened lime hydrates very slowly.

The unfastened lime blanketed with the aid of using a skinny movie of cement. This prevents direct touch among lime and water. After the paste has set, moisture penetrates the unfastened lime, and hydration starts. The slaked lime occupies a huge volume. Hence enlargement takes place. Thus the mortar and urban crafted from unsound cement may also broaden cracks after a few time.
Consistency of Cement: The bodily kingdom of cement paste is referred to as consistency.
The motive of the consistency take a look at is to estimate the amount of blending water to shape a paste of everyday consistency. It is measured via way of means of the Vicat equipment Test. If the water content material withinside the cement paste is such that the Vicat’s plunger penetrates as much as five to 7 mm from the lowest of the mould, the cement paste is referred to as to be of everyday consistency.

Q6) Explain Soundness test in detail.

A6)

Fig: Soundness test apparatus

The soundness of cement suggests the steadiness of any cement throughout the extent extrade withinside the procedure of putting and hardening. In case the extent extrade in cement is volatile after putting and hardening, the concrete detail will crack, which could have an effect on the high-satisfactory of the shape or maybe motive critical accidents, referred to as terrible dimensional stability.
The soundness take a look at of cement determines the enlargement of cement after it begins offevolved placing. Certain cement has been located to go through a huge enlargement after placing inflicting disruption of the set and hardened mass. This enlargement of cement can reason extreme issues for the sturdiness of systems whilst such cement is used.
The soundness of cement is in particular measured through methods: EN-196 (1995), that's primarily based totally at the Le Châtelier take a look at method, and the autoclave take a look at (ASTM-C151, 2015), wherein strain is likewise implemented to the sample.
Significance of Soundness of Cement
The trying out of the stability of cement, to make sure that the cement does now no longer display any considerable next enlargement of high importance.

The unsoundness is taking place specifically because of an extra lime that might be mixed with acidic oxide on the kiln.

This is likewise because of insufficient burning or inadequate fineness of grinding or thorough blending of uncooked materials.

It is likewise may also arise because of too excessive share magnesium content material or calcium sulfate content material may also motive unsoundness in cement.

Q7) Explain rapid hardening cement.

A7)

Rapid Hardening Cement

Rapid hardening cement attains excessive power withinside the early days; it's miles utilized in concrete in which formworks are eliminated at an early degree and are much like everyday portland cement (OPC).
This cement has elevated lime content material and carries better c3s content material and finer grinding, which offers better power improvement than OPC at an early degree.
The power of fast hardening cement on the 3 days is much like 7 days power of OPC with the identical water-cement ratio. Thus, the benefit of this cement is that formwork may be eliminated earlier, which will increase the charge of creation and reduces the value of creation with the aid of using saving formwork value.

Q8) Explain Portland pozzolones cement and Portland flyash cement.

A8)

Portland pozzolones cement

Portland pozzolana cement is ready via way of means of grinding pozzolanic clinker with Portland cement. It is likewise produced via way of means of including pozzolana with the addition of gypsum or calcium sulfate or via way of means of in detail and uniformly mixing Portland cement and satisfactory pozzolana.
This cement has a excessive resistance to diverse chemical assaults on concrete as compared with regular portland cement, and thus, it's far extensively used.
It is utilized in marine structures, sewage works, sewage works, and for laying concrete underwater, along with bridges, piers, dams, and mass concrete works, etc

Portland flyash cement

Fly ash may be used as high cloth in lots of cement-primarily based totally products, along with poured concrete, concrete block, and brick. One of the maximum not unusualplace makes use of of fly ash is in Portland cement concrete pavement or PCC pavement.
Road creation initiatives the use of PCC can use a extremely good deal of concrete, and substituting fly ash affords extensive monetary benefits. Fly ash has additionally been used as embankment and mine fill, and it has an increasing number of won reputation via way of means of the Federal Highway Administration.
The fee of substitution—of fly ash for Portland cement—usually exact is 1 to at least one half kilos of fly ash for 1 pound of cement.1 Accordingly, the quantity of high-quality mixture withinside the concrete blend need to be decreased to deal with the extra quantity of the fly ash.

Q9) Define Field test

A9)

Date of Manufacturing: As the power of cement reduces with age, the date of producing of cement baggage need to be checked. Cement Color: The colour of cement need to be uniform. It need to be common cement colour i.e. grey colour with a mild greenish shade.
Whether Hard Lumps are Formed: Cement need to be unfastened from difficult lumps. Such lumps are shaped via way of means of the absorption of moisture from the atmosphere. T
Temperature Inside Cement Bag: If the hand is plunged right into a bag of cement, it need to be cool in the cement bag. If hydration response takes area in the bag, it turns into warm.
Smoothness Test: When cement is touched or rubbed in among fingers, it need to deliver a clean feeling. If it felt rough, it shows adulteration with sand.
Water Sinking Test: If a small amount of cement is thrown into the water, it need to glide a while earlier than in the end sinking.
The odor of Cement Paste: A skinny paste of cement with water need to sense sticky among the fingers. If the cement incorporates too much-pounded clay and silt as an adulterant, the paste will deliver an earthy odor.
Glass Plate Test: A thick paste of cement with water is made on a chunk of a tumbler plate and it's miles stored below water for twenty-four hours. It need to set and now no longer crack.
Block Test: A 25mm × 25mm × 200mm (1”×1”×8”) block of cement with water is made. The block is then immersed in water for 3 days. After removing, it's miles supported 150mm aside and a weight of 15kg uniformly positioned over it. If it suggests no signal of failure the cement is good.

Q10) What are the sources of aggregate?

A10)

Sources of aggregates

Aggregates are the maximum critical parts in concrete. They deliver frame to the concrete, lessen shrinkage and impact economy. Natural aggregates are inert granular substances along with sand, gravel stone or overwhelmed stone which might be used with a binding medium i.e. water, bitumen, portland cement, lime, etc. to shape compound substances i.e. asphalt concrete and portland cement concrete.
Almost all of the herbal combination substances originate from mattress rocks. There are 3 kinds of rocks; igneous, sedimentary and metamorphic. These classifications are primarily based totally at the way of formation of rocks. It can be recalled that igneous rocks are fashioned through the cooling of molten magma or lava on the floor of the crest (lure and basalt) or deep below the crest (granite).
They are hard, hard and dense.
They can be acidic or fundamental relying upon the proportion of silica content.
They can also additionally arise in mild hues or darkish hues. The sedimentary rocks are fashioned under the ocean mattress and finally lifted up. Sedimentary rocks range from smooth to hard, porous to dense and mild to heavy.
The diploma of consolidation, the sort of cementation, the thickness of layers and contamination, those all are vital elements to decide the suitability of sedimentary rock for concrete aggregates.
Metamorphic rocks are at first both igneous or sedimentary rocks which can be finally metamorphosed because of severe warmth and pressure. Many metamorphic rocks specially quartzite and gneiss were used for the manufacturing of right concrete aggregates.
The concrete making homes of herbal aggregates are prompted to a degree on the idea of geological formation of the discern rock collectively with the following procedures of weathering and alteration.

Q11) Give classification and nomenclature of aggregates.

A11)

Classification of aggregates primarily based totally on: Grain Size If you separate aggregates through length, there are overriding categories:
Fine Coarse

The length of first-class aggregates is described as four.75mm or smaller. That is, aggregates which may be surpassed thru quite a number four sieve, with a mesh length of four.75mm. Fine aggregates encompass matters inclusive of sand, silt and clay. Crushed stone and beaten gravel can also fall below this category.

Typically, first-class aggregates are used to enhance workability of a concrete mix.
Coarse aggregates degree above the four.75mm limit. These are much more likely to be herbal stone or gravel that has now no longer been beaten or processed. These aggregates will lessen the quantity of water wanted for a concrete mix, which might also lessen workability however enhance its innate strength.
Classification of aggregates primarily based totally on:

Density :There are 3 weight-primarily based totally versions of aggregates: Light weight Standard High density Different density aggregates can have a whole lot exceptional applications. Lightweight and extremely light-weight aggregates are extra porous than their heavier counterparts, in order that they may be positioned to high-quality use in inexperienced roof construction, for example.

They also are utilized in mixes for concrete blocks and pavements, in addition to insulation and fireproofing. High density aggregates are used to shape heavyweight concrete. They are used for whilst excessive strength, long lasting concrete systems are required – constructing foundations or pipework ballasting, for example.

Q12) Define Coarse and fine aggregate.

A12)

	Scopes	Fine Aggregate (FA)	Coarse Aggregate (CA)
1	Definition	Fine aggregates are small size filler materials in construction.	Coarse aggregates are larger size filler materials in construction.
2	Size of Particles	Fine aggregates are the particles that pass through 4.75 mm sieve and retain on 0.075 mm sieve.	Coarse aggregates are the particles that retain on 4.75 mm sieve.
3	Materials	Sand, surki, stone screenings, burnt clays, cinders, fly ash, etc are used as fine aggregate in concrete.	Brick chips (broken bricks), stone chips (broken stones), gravels, pebbles, clinkers, cinders etc. are used as coarse aggregate in concrete.
4	Sources	River sand or machine sand, crushed stone sand, crushed gravel sand are the major sources of fine aggregate.	Dolomite aggregates, crushed gravel or stone, natural disintegration of rock are the major sources of coarse aggregate.
5	Surface Area	The surface area of fine aggregates is higher.	The surface area of coarse aggregate is less than fine aggregates.
6	Function in Concrete	The voids between the coarse aggregate are filled up by fine aggregate.	Coarse aggregate acts as inert filler material for concrete.
7	Uses	Fine aggregates are used in mortar, plaster, concrete, filling of road pavement layers, etc.	Coarse aggregates are mainly used in concrete, railway track ballast, etc.

Q13) What is normal weight (light and heavy weight aggregates)?

A13)

Normal weight aggregates, used for most concretes, are naturally occurring gravels from land or marine sources, or crushed rocks, for example, limestone, granite or basalt.
Used in maximum concrete construction, normal-weight aggregates are received with the aid of using draining riverbeds or mining and crunching formational cloth. Concrete made with normal-weight excellent and coarse aggregates usually weights approximately a hundred and forty four lb / ft3. Boulders and cobbles are usually now no longer used of their as-mined length however are overwhelmed to make numerous sizes of coarse mixture and synthetic sand and mineral filler.
Gravels and clearly going on sand are produced with the aid of using the movement of water and weathering on glacial and river deposits. These substances have round, easy surfaces and particle-length distributions that require minimum processing.
These substances may be provided in both coarse or excellent-mixture sizes. Fine aggregates have 100% in their cloth passing the 3â„8-in sieve. Coarse aggregates have the majority of the cloth retained at the No. Four sieve. Aggregates incorporate the finest extent percent in portland-cement concrete, mortar, or asphaltic concrete.
In a portland-cement concrete blend, the coarse and excellent aggregates occupy approximately 60 to seventy five% of the overall blend extent. For asphaltic concrete, the aggregates constitute seventy five to 85% of the combinationture extent. Consequentially, the aggregates aren't inert filler substances. The person mixture homes have demonstrable consequences at the provider lifestyles and sturdiness of the cloth gadget wherein the mixture is used, along with portland-cement concrete, asphaltic concrete, mortar, or mixture base.
The acceptability of a rough or excellent mixture to be used in concrete or mortar is judged with the aid of using many homes which includes gradation, quantity of excellent cloth passing the No. 2 hundred sieve, hardness, soundness, particle shape, extent stability, ability alkali reactivity, resistance to freezing and thawing, and natural impurities.
For aggregates utilized in widespread constructing construction, belongings limits are supplied in ASTM C33, Specification for Concrete Aggregates, C637, Specification for Aggregates for Radiation-Shielding Concrete, and C330, Specification for Lightweight Aggregates for Structural Concrete.
For different sorts of construction, along with highways and airports, requirements written with the aid of using numerous change or governmental agencies are available.

Q14) Explain aggregate characteristics and their significance in strength.

A14)

Concrete is a combination of cementious cloth, combination, and water. Aggregate is typically taken into consideration inert filler, which money owed for 60 to eighty percentage of the extent and 70 to eighty five percentage of the load of concrete.
Although combination is taken into consideration inert filler, it's miles a vital aspect that defines the concrete’s thermal and elastic residences and dimensional stability.
Aggregate is assessed as unique types, coarse and first-rate. Coarse combination is normally extra than four, .seventy five mm (retained on a No. Four sieve), at the same time as first-rate combination is much less than four.seventy five mm (passing the No. Four sieve).
The compressive combination power is an crucial thing withinside the choice of combination. When figuring out the power of regular concrete, maximum concrete aggregates are numerous instances more potent than the opposite additives in concrete and consequently now no longer a thing withinside the power of regular power concrete.
Lightweight combination concrete can be extra inspired with the aid of using the compressive power of the aggregates. Other bodily and mineralogical residences of combination have to be acknowledged earlier than blending concrete to achieve a suited combination.
These residences consist of form and texture, length gradation, moisture content, precise gravity, reactivity, soundness and bulk unit weight. These residences along side the water/cementitious cloth ratio decide the power, workability, and sturdiness of concrete.
The form and texture of combination influences the residences of clean concrete extra than hardened concrete. Concrete is extra attainable whilst easy and rounded combination is used in preference to tough angular or elongated combination.
Most herbal sands and gravel from riverbeds or beaches are easy and rounded and are superb aggregates. Crushed stone produces a lot extra angular and elongated aggregates, that have a better floor-to-extent ratio, higher bond traits however require extra cement paste to provide a attainable combination.
The floor texture of combination may be both easy or tough. A easy floor can enhance workability, but a rougher floor generates a more potent bond among the paste and the combination growing a better power.
The grading or length distribution of combination is an crucial feature as it determines the paste requirement for attainable concrete. This paste requirement is the thing controlling the cost, given that cement is the maximum highly-priced aspect.
It is consequently suited to decrease the quantity of paste constant with the manufacturing of concrete that may be handled, compacted, and completed at the same time as presenting the vital power and sturdiness.
The required quantity of cement paste relies upon the quantity of void area that have to be crammed and the whole floor location that have to be covered. When the debris are of uniform length the spacing is the greatest, however whilst a number of sizes is used the void areas are crammed and the paste requirement is lowered.
The extra those voids are crammed, the much less attainable the concrete becomes, consequently, a compromise among workability and economic system is vital.

Q15) Explain size & grading of aggregate strength of aggregates.

A15)

‘Aggregate’ is a time period for any particulate material. It consists of gravel, beaten stone, sand, slag, recycled concrete and geosynthetic aggregates. Aggregate can be natural, synthetic or recycled.
Aggregates make up a few 60 -80% of the concrete blend. They offer compressive electricity and bulk to concrete.
Aggregates in any precise blend of concrete are decided on for his or her durability, electricity, workability and cappotential to acquire finishes.
For an amazing concrete blend, aggregates want to be clean, hard, sturdy debris freed from absorbed chemical compounds or coatings of clay and different first-class substances that might purpose the deterioration of concrete.
Aggregates are divided into either ‘coarse’ or ‘first-class’ categories. - Coarse aggregates are particulates which might be more than 4.75mm. The ordinary variety hired is among 9.5mm and 37.5mm in diameter. - Fine aggregates are generally sand or beaten stone which might be much less than 9.55mm in diameter.
Typically the maximum not unusualplace length of combination utilized in creation is 20mm. A large length, 40mm, is extra not unusualplace in mass concrete.
Larger combination diameters lessen the amount of cement and water needed.