PROPERTIES OF PROPERTIES OF CONCRETECONCRETE

ARTICLEARTICLE

Effects of aggregates on Effects of aggregates on properties of concreteproperties of concrete

• SUBMITTED TO:• Dr. Ayub Elahi

• SUBMITTED BY:

• 2K9-SCET-02/CIVIL• 2K9-SCET-26/CIVIL• 2K9-SCET-07/CIVIL• 2K9-SCET-52/CIVIL• 2K9-SCET-54/CIVIL

• Aggregates

 Granular mineral material(such as sand, gravel, crushed stone) used with a bonding medium (such as cement or clay) to make concrete, plaster, or terrazzo mixture.

Sum minerals are given below:

• Minerals

Silica (ex. Quartz)

• Silicates (ex. Clay)

• Carbonate (ex. Calcite, dolomite).

Types of aggregatesTypes of aggregates

1.Fine aggregates

2.Coarse aggregats

Properties of aggregates and Properties of aggregates and their effects on concretetheir effects on concrete

• Grading:

Grading is the distribution of particles

among various sizes. Grading is usually expressed in terms of cumulative percentage passing each sieve.

Coarse Aggregate Grading:

• Usually more water and cement is required for small-size aggregate than for large sizes,due to an increase in total aggregate surface area.

• Grading sieves

• The optimum maximum size of coarse

aggregate for higher strength depends on

1.Relative strength of the cement paste

2. Cement-aggregate bond

3.Strength of the aggregate particles

• Effect of Size on concrete:

• Variation in the size of Aggregates changes the water demand, cement content, micro-cracking (strength) in concrete. It also effects pumpability, and durability of concrete.

Effect of Size on concreteEffect of Size on concrete

• The larger the maximum size of the coarse aggregate, the lower the water demand of the mix. The maximum size of aggregates is important parameters in any concrete mix. its affect relative proportions in mix, workability, economy, porosity and shrinkage of concrete etc

Effect of Grading on concreteEffect of Grading on concrete

• Grading of aggregates depends on the proportions of coarse and fine aggregate. If grading of aggregate is varied, it also changes cement paste content (cost economy), workability of the mix, density and porosity

MaximumMaximumaggregate size, they affectaggregate size, they affect

• Relative aggregate proportions

• Cement and water requirement

• Workability

• Pump ability

• Economy

Fineness modulusFineness modulus

• is a measurement of the coarseness or fineness of a given aggregate. For a fine aggregate, FM is calculated from the cumulative percentages of aggregate retained on sieves No.4,8, 16, 30, 50, 100, 3/8in., 3/4in., 1.5in., 3in., and 6in., divided by 100. The Fineness Modulus should be between 2.3 and 3.1.

Effect of Fineness on Density of Effect of Fineness on Density of ConcreteConcrete

• After measuring the slump, several 150 mm cubes were filled. These were cured in water tank for 28 days. After curing, each cube was weighed using electronic balance and density of concrete was calculated.

TextureTexture

• The surface texture of aggregate can be either smooth or rough

Effects of Surface Texture Effects of Surface Texture

• The surface texture of aggregate can be either smooth or rough. A smooth surface can improve workability, yet a rougher surface generates a stronger bond between the paste and the aggregate creating a higher strength

• Rough-textured and elongated particles require more cement paste to produce workable concrete mixtures, thus increasing the cost

• The shape and texture of aggregate affects the properties of fresh concrete more than hardened concrete. Concrete is more workable when smooth and rounded aggregate is used instead of rough angular or elongated aggregate. Most natural sands and gravel from riverbeds or seashores are smooth and rounded and are excellent aggregates. Crushed stone produces much more angular and elongated aggregates, which have a higher surface-to-volume ratio, better bond characteristics but require more cement paste to produce a workable mixture.

Absorption and Surface MoistureAbsorption and Surface Moisture

• The absorption and surface moisture ofaggregates should be determined usingASTM C 70, C127, C128, and C 566 so thatthe total water content of the concrete can becontrolled and the batch weights determined

The moisture conditions of aggregates are:• Oven dry• Air dry• Saturated surface dry (SSD)• Damp or wet

Effects of absorption & Surface Effects of absorption & Surface Moisture Moisture

• that using saturated coarse aggregate in the mix, always

yields higher shrinkage strain than is dry aggregate. There about 10% increase in drying shrinkage for all mixes, except in uncrushed gravel.The increase for uncrushed gravel was about 3% and that could be resulted from the low water absorption (0.98%) and smooth surfaces which make no difference between dry and saturated condition.

Effects of absorption & Surface Effects of absorption & Surface Moisture Moisture

• Using dry aggregate causeds the water/cement ratio in the vicinity of the aggregate particles to be less than else where because aggregate absorbed water to reach saturated surface-dry condition

Moisture conditions of aggregate

• The reduction in water content would improve the bond between cement mortar and aggregate and reduce the interface zone porosity and microcracking (2), and consequently,increases the restraining action of

aggregate against drying shrinkage.The same influence was observed with respect to the elasticity modulus,compressive, and splitting tensile strength of concrete. For porcilinite aggregate, the effect of moisture content was more obvious on elasticity modulus and splitting tensile

RefrencesRefrences

• www.ads google.com• NEVILLE, A.M, 'Properties of concrete', IV

edition, Pearson Education Pvt. Ltd. 2005.• www.engg pedia .com• http://books.google.com.pk/books?id=TNzk-

4WA6GoC&lpg=PA412&ots=EV2yFWPT9A&dq=effects%20of%20fineness%20modulous%20on%20conc&pg=PA412#v=onepage&q&f=false

• Slides of lecture