Experimental analysis of Component Interaction in concrete

PRINCE SHRI VENKATESHWARA PADMAVATHY ENGINEERING

COLLEGE(affiliated to Anna University)

VIII SEMESTER PROJECTCIVIL DEPARTMENT

HARISH.RSATHYANARAYANAN.R

VANCHINATHAN.M

GUIDED BY SNEKHA.G

Experimental analysis of Component Interaction in Concrete

Abstract This project focuses on increasing the characteristic

compressive strength of concrete through the simplest and cheapest means possible. To achieve this, the interaction of components present in the concrete are to be studied and with this information, minor changes can be made to enhance the performance of concrete.

Scope This project is an experimental study of the

component interaction in concrete. Irrespective of the results, this project will provide a clearer view of the internal workings of cement, fine aggregate and coarse aggregate which can be used for future experiments and innovations.

If successful, this project is a breakthrough in concrete technology. The possibility of producing a High Performance Concrete without chemical admixtures or extra materials will be widely accepted. The compressive strength of the concrete will be significantly increased.

Methodology

Component Interaction

Phase – I Aggregat

ePhase – II

SandPhase – III Water

PHASE – IAGGREGATE

Failure in Concrete The strength of concrete depends on

three parameters; Strength of cement matrix Strength of aggregate Strength of cement matrix – aggregate

bond. Various experimental analysis have

proven that the strength of the bond between the cement matrix and the aggregate is the lowest.

The percentage of failure, due to crack passing through the aggregate – cement matrix bond is almost 100%.

Testing of theory

Testing of theory

The source of the crack is at the extreme fibre of the member. The crack then travels inwards. The width of the crack is directly proportional to the depth it travels. It is clear from this electron microscope image that the bond is the weakest part of the member.

Crack Propagation

Click icon to add picture“Experimental Mechanics And Physics Of Small Scale Materials And Interfaces” by Baoming Wang, Raghu Pulavarthy & Tarek Alam

Aggregate Surface The cement and sand mix together well

and act homogeneous due to similar particle size. They possess COHESION.

The particle size at the surface of the aggregates are very large when compared to the cement matrix and therefore the surface of the aggregate acts like a wall, and does not bond with the matrix.

To increase this bond, the ADHESION between the aggregate and the matrix must be increased.

Aggregate Surface

This is a doping image of a cut section of concrete.

Wall Effect of Aggregate

“The Scientific Electronic Library Online”

Interfacial Transition Zone Due to this wall effect, the cement

particles and water molecules accumulate around the aggregate and form a weak zone called the interfacial transition zone.

This zone is present at about 15 to 20 microns away from the surface of the aggregate.

This zone of higher water content and improper mixing of cement matrix is the region of crack propagation and must be reduced.

The size of the aggregate also affects the zone. This zone creates minor micron level cracks around the aggregate even before the load is applied and hence will be used by the crack during propagation. These micro cracks grow with time.

Interfacial Transition Zone“Examination With The Stereomicroscope” by FHWA

The phase – I Experiment The objective of this phase is to reduce

the ITZ. This is going to be done by decreasing

the particle size at the surface of the aggregate.

By increasing the roughness of the surface, the bonding or gripping of aggregate with cement will increase.

This will also increase the interlocking of the aggregates which take up about 33 to 50% of the shear capacity of concrete.

The size and shape of the aggregate also affects it.

Abrasion

Abrasion

Properties of aggregatesTEST NORMAL

AGGREGATEABRASED

AGGREGATE

Water Absorption 1.19% 1.47%

Impact Value 6.15% 7.50%

Specific Gravity 2.74 2.74

Abrasion Value 4.70% 4.50%

Crushing value 30.95% 30.85%

Increase in water absorption

Literature review1. “Influence of interface properties

on fracture behaviour of concrete” by G.Appa Rao and Raghu Prasad. This report explained the importance of the interface concrete between mortar and aggregate.

2. “Surface preparation for improved adhesion” published by “March plasma Systems” showed the necessary requirements for a surface to increase the adhesion property.

PHASE – IIFINE AGGREGATE

Voids in concrete There are two kinds of voids,

Air voids formed in cement matrix. Voids in between aggregates.

The air voids have to be kept to a minimum but should not be very low.

The voids in between aggregates are formed due to improper particle size distribution of fine aggregate.

These voids are filled only by cement and no sand and hence can be easily penetrated by cracks.

Air Voids

The area below the crack clearly shows the well mixed cement – sand matrix behaving as a solid block. Where as in between the two aggregates at the top, no sand particles are present and hence letting the crack penetrate easily.

Crack propagation through weak cement paste

“Visual Inspection of Concrete”by Nick Gromicko and Kenton Shepard

Gradation The way particles fit together in the mix,

as influenced by gradation, has an important effect on the workability of fresh concrete and the strength and durability of hardened concrete.

There are three types of gradations; Poorly graded Gap graded Well graded

Out of these three, a well graded mixture has the most strength.

Gradation

The voids formed by a larger size particle must be filled by the particle of one or two sizes smaller and so on.

Effects of proper gradation

Effects of gradation Increasing the gradation of the mixture

results in; Greater surface area of the sand. An increase in the packing and density of the

mixture. An increase in aggregate – cement ratio. A decrease in the water content of the

mixture. All of which results in increase in strength of

concrete. The requirements of gradation are clearly

stated in IS 383.

The Phase – II Experiment The objective of this phase is to increase

the gradation of the concrete. Apart from this increasing the strength of

concrete individually, when considering the PHASE – I , this gradation will work with more efficiency as the particle size on aggregate surface is lower than before.

This gradation is going to be done by increasing the coarseness of sand by experimenting with different sizes and fineness moduli.

Literary review “Chapter 5 : Aggregates of

Concrete” by “The University of Memphis, PCA manual”. This report very thoroughly explains everything about the aggregates used in concrete. The concept of well graded mixture was taken from this.

“The Effects Of Aggregates Characteristics On The Performance Of Portland Cement Concrete” by the “ICAR”. The characteristics and the effects of aggregates

PHASE – IIIWATER

Function of water Water is a very important component in

concrete as it has many functions. Water helps form the cement gel which

is a primary contributor to the strength of concrete.

Water is the agent that cement uses to bind the other two main components together.

Concrete achieves it’s strength through a process called hydration, which in simple terms is the reaction between water and cement.

Water and Adhesion Water plays a key role in increasing the

adhesion between two dissimilar surfaces.

Apart from the properties of the surfaces that influence adhesion, water influences it too especially when one surface has its main component as water. (cement matrix)

The property of water that has an effect on this is called wettability.

Wettability Wettability is the property of water to

spread over a surface with minimal surface tension.

Liquids with high surface tension usually spread lesser and thus will not increase the adhesion between two surfaces.

Wettability The wettability of water can be

increased by decreasing the contact angle of water.

This is done using Surfactants. Surfactants are also used in soaps,

shampoos, detergents, etc to cover larger area of the dirt and or stain.

Combined with the increased roughness of the aggregate the thesis is that the adhesion will increase between aggregate and matrix.

Increase in wettability Scientist Wenzel created a theoretical

model of increased wettability when the surface of the body is rough.

This is the theory we have used.

The Phase – III Experiment

The objective of this phase is to increase the wettability of water used.

This, combined with the existing two phases will increase the strength of concrete.

A cheap and abundant biosorbent like the oil obtained from coconut coir, wheat gram, waste frying oil, etc has good surfactant properties and will be analyzed and adopted for this experiment.

Literary review “Surfactant chemistry and general

phase behaviour”. This gave the basics of what a surfactant does.

“Low Cost Production Of Biosurfactant From Different Substrates” by Samadhan Waghmode, Chandrashekhar Kulkarni, Sneha Shukla, Priyanka Sursawant, Chaitanya Velhal.

Tentative ScheduleWEEK WISE

SPLIT OBJECTIVES OF THE WEEK

WEEK 1 Phase – 1 analysis. Aggregate abrasion

WEEK 2 Phase – 2 analysisAbrased aggregate properties

WEEK 3 Phase – 3 analysisPhase – 1 casting

WEEK 4 Phase – 2 castingPhase – 3 casting

WEEK 5 Combined Analysis