Concrete

concrete

a proportioned mixture of cement, aggregate, and water.

6,500 B.C.

This year was roughly when the first concrete-like buildings were made.

6,500 B.C.

Bedouins created these historical concrete structures in modern-day Syria and Jordan.

3,000 B.C.

During this time, Egyptians used mud mixed with straw to create an adobe-like building material.

3,000 B.C.

They also developed and used gypsum and lime mortars to bind the adobe bricks together. Around the same time, builders in China were using a form of cement created with sticky rice

700 B.C.

The Bedouins discovered cement that hardens underwater and created kilns for producing mortar around this time. They used that mortar to help construct floors, houses and other structures. During this time, they also began tamping the concrete material and had an understanding that the substance wouldn’t work as well if it were too saturated

600 B.C.

The Greeks discovered a natural substance that can create concrete when they mixed it with lime. While they got use out of the substance, they weren’t as advanced with concrete techniques as other cultures were.

200 B.C.

By this time, the Romans had perfected building with concrete, though in a different way than we use it today. The Romans would create most of a structure with loose rocks and material, cementing them together with mortar. They even used cosmetic bricks in combination with their version of cement. Using non-structural blocks established concrete as a purposeful and aesthetic product.

1414

The collapse of the Roman Empire made the interest in concrete dormant until manuscripts explaining the substance resurfaced during this year. With that, came a new appreciation for the building material. This year serves as one of the many turning points in the history of concrete. It started the chain reaction for the discovery of new ways to make and use concrete for centuries to come.

1793

John Smeaton created a more efficient method of producing hydraulic lime in 1793. The product was used to help cement set, and the modernized production made it easier to make concrete and have it set quickly.

1824

This year was very vital in the history of concrete because it’s whenbricklayer Joseph Aspdincreated Portland cement. Named as such because it was similar to building stones in Portland, England, Portland cement was a strong form of the building material. Aspdinproduced the cement by burning chalk and clay in a kiln. He later decided to add limestone to the clay to create clinker

concrete

a plastic mass which can be cast, molded or formed into predeterminedsizeorshape

concrete

upon hydration, becomes stone-like in strength, hardness and durability.

setting

The hardening of concrete is called

mortar, stucco or cement plaster

concrete when mixed with water and a fine aggregate of less than 6mm (1/4’) is known as

concrete

when mixed with water, fine aggregate, and a large aggregate of more than 6mm (1/4”) in size produces what

reinforced concrete

concrete when strengthened by embedded steel is called

plain or mass concrete

concrete when without reinforcement

concrete compressive strength, durability, permeability, and dimensional changes

qualities of a good concrete

w/c ratio, quality, degree of compaction, age, temp and period of curing

Crushing strengthof a fully compacted concrete depends upon;

joseph aspdin

Created the portland cement

concrete compressive strength

Strength in crushing tension, flexure, and bond

durability

resistance to weathering, adverse chemical reactions, and wear

impermeability

water tightness, and resistance to corrosion of reinforcement

Properties involving dimensional changes

minimum drying shrinkage, minimum length change due to temperature, freedom from cracks, extensibility

Weathering

due to exposure to the natural atmospheric condition

chemical reactions

can weaken the strength of concrete

wear

causes deformation or damage as a result of long term use

selection of materials, proportioning, mixing, transporting and placing, curing and protection after placed

Qualities of good concrete can be obtained through (6-7)

cement, aggregates, water

materials for concrete

high-grade portland cement conforming to the standard specifications and test for portland cement of the ASTM

Reinforced-concrete construction should be in what cement

american society for testing materials

meaning of ATSM

apprx. 1 cu. ft. 94 lbs

each bag of cement is equivalent to

soundness (consistency of volume), time of setting, fineness, tensile strength

what are the kind of tests for the standard specifications and test for portland cement

aggregate

are inert mineral fillers used with cement and water in making concrete, should be particles that are durable strong, clean, hard and uncoated , and which are free from injurious number of dusts, lumps, soft and flaky particles, shale, alkali, organic matter loam or other deleterious substances .

fine aggregates

consist of sand, stone screenings or other inert materials of similar characteristics

smaller than 6mm (1/4”)

size of fine aggregates

80% to 95%; NO. 4 wire sieve and not > 30% < 10%; No. 50 sieve

requirements for fine aggregates

Coarse aggregates

consists of crushed stones, gravel other inert materials of similar

larger than ¼” in size but not exceed 25mm (1”) up to 50mm (2”) for less highly reinforced parts

size of coarse aggregative

Special aggregates

aggregates such as cinders, blast furnace slag, expanded shale or clay, perlite, vermiculite, and sawdust, may produce:

➢ lightweight, nailable concrete

➢ thermal insulating concrete.

water

should be free from oil, acid, alkali, vegetable matter, or other deleterious substances

sea or brackish water

what type of water is not allowed for concrete

water

combines with the cement to form a paste which coats and surrounds the inert particles of aggregates. Upon hardening, it binds the entire mass together.

water-cement (w/c) ratio

is the amount of water used per bag of cement.

plastic and workable.

ideal mix of concrete

5 to 7 gallons, with 6.5 gallons as average

w/c ratio varies to what

slump test

used for measuring the consistency of a concrete mix .

consistency

“state of fluidity of the mix”, and it includes the entire range of fluidity from

slump test

In this test the tendency of a mix reduce its height due to gravity action, is measured.

metal cone (200mm 8” dia - 100mm 4” dia) 300mm (12”) height

main apparatus for slump test

12mm (½”)

length of rod in slump test

harsh mix

mix efficient for slabs, pavements, or mass concrete where the lowest possible water-cement ratio is desirable

125mm (5”)-50mm (2”)

SLUMP TEST: Reinforced foundation walls andfootings

100mm (4”)-25mm (1”)

SLUMP TEST: Plain footings, caissons, and substructure walls

150mm (6”)-75mm (3”)

SLUMP TEST: Slabs, beams, thin reinforced walls & building columns

75mm (3”)-25mm (1”)

SLUMP TEST” Pavements and floor laidon ground

75mm (3”)-25mm (1”)

SLUMP TEST: Heavy mass construction

good quality materials, w/c ratio, slump test, correct proportions, workable mix

Briefly stated, the principles of proper proportioning are as follows

water-cement ratio

strength of a workable concrete mix depends upon what

economy

depends upon the proper proportioning of the fine and coarse aggregates

arbitrary proportions, water-ratio and slump test, water-ratio, slump and fineness modulus

proportioning of concrete methods

arbitrary selection

is the oldest, the most commonly used, the most convenient and the least scientific method to proportion concrete

arbitrary selection

In this method, the aggregates are measured by loose volume, that is, its volume as it is thrown into a measuring box (1ft x 1ft)

cement:sand:gravel

parts of concrete proportion by arbitrary selection

AA 1:1.5:3

class and proportion for concrete under water, retaining walls

A 1:2:4

class and proportion for concrete For suspended slabs, beams, columns, arches, stairs, walls of 100mm (4”) thickness

B 1:2.5:5

class and proportion for concrete For walls thicker than 100mm (4”), footings, steps, reinforced concrete slabs on fill.

C 1:3:6

class and proportion for concrete For concrete plant boxes, and any non-critical concrete structures.

D 1:3.5:7

class and proportion for concrete For mass concrete works

Proportioning by the water-ratio and slump test

There are two steps to be observed: • Select the amount of water to be added to the cement to give the desired strength (see Table) • Add just enough mixed aggregate to the water and cement to give a concrete mix the desired consistency

Proportioning by water-ratio, slump, and fineness modulus

same as the second proportioning method except that the proportions of the fine and coarse aggregate are determined by the fineness modulus method

Machine Mixing and Mixing by Hand

types of mixing of concrete

continuous mixers

into which the materials are fed constantly and from which the concrete is discharged in a steady stream

drum mixers

most common type of machine mixing

mixing by hand

cement and fine aggregate shall first be mixed dry until the whole is a uniform color. • water and coarse aggregate shall then be added, and the entire mass turned at least three times, or until a homogeneous mixture of the required consistency is obtained.

1 to 3 hours after mixing

initial set of concrete takes place at what

Regaging or retempering

of concrete that has been allowed to stand more than ½ hour is not to be permitted

30 minutes

The time of transportation of concrete should not exceed

over 5 ft. for unexposed work and over 3 ft. for exposed work

Concrete should never be allowed to drop freely at what height

reinforcement

what can be placed to minimize shrinkage of concrete due to hardening and contraction from temperature changes, causes cracks the size of which depends on the extent of the mass.

shrinkage or contraction joints

it is better to place this In long continuous length of concrete

Shrinkage cracks

are likely to occur at joints where fresh concrete is joined to concrete which has already set, and hence in placing the concrete, construction joints should be made on horizontal and vertical lines.

Hardening

is a rather slow process in which the cement and water unite to form compounds that give strength and durability to the concrete. It continues if the temperatures are favorable, and moisture is present.

age or time, temp, moisture

Three main factors that affect hardening

7 days

In order that the hardening may proceed favorably, the fresh concrete, for about _ days after placing, should be protected from, excessive vibration, loads, extreme heat or cold, too rapid drying, and contact with impurities which may interfere with the chemical action

28 days (60% of maximum value) and 3 months (80% of mv)

The compressive strength reaches about how long and how many percent of maximum value

covering, removal of forms at pescribed time, sprinkling of water, admixtures

how to keep concrete from drying too rapidly

curing

consists primarily in keeping the concrete from drying out too rapidly.

admixtures

Substances added to cements, mortars, and concrete for the purpose of improving or imparting particular properties

mixing into concrete, mortar or those for surface application or finish.

three categories of admixtures

powder, paste, liquid form

how does admixtures come in

accelerators, retarders, air-entraining agents, inert, waterproofing, colored pigments

concrete admixtures include (6)

Accelerators

to speed up setting time, to develop earlier strength, and to reduce length of time for protection. Principal ingredients are calcium chloride. Maximum amount added is 2 lbs. per bag of cement.

Retarders

to slow down the hydration of the cement during very hot weather. Principal ingredients include zinc oxide, calcium lignosulfonate, derivatives of adipic acid.

Air-entraining agents

introduce minute air bubbles to greatly increase the resistance of concrete to freezing and thawing, increase plasticity and reduce bleeding. Addition of air-entraining admixtures is usually in the proportion of 3 to 6% of the volume of concrete. They aremanufactured from such ingredients as rosin, beef tallow, stereates, foaming agents (soap).

Inert

finely divided powders such as powdered glass , silica sand, stone dust, hydrated lime-are added to improve workability, used as per manufacturer’s directions. Hydrated lime is usually in the proportion of 10 to 15% of the cement by volume.

Waterproofing (permeability-reducing)compounds

reduce the capillary attraction of the voids in the concrete or mortar, but while it may decrease water absorption of the concrete or mortar, it does not render concrete waterproof. They are manufactured from stearic acid or its compounds, mainly calcium steareate, and include asphalt emulsions. They are introduced usually in the amounts of 0.1 to 4.0% of the weight of cement.

Colored pigments

are mainly to used to give color to concrete floors. There are two types

dry cast (broadcast or dust-on) and integral colors

two types of colored pigments admixtures