Measuring the cement content of hardened concrete is useful to assess the concrete's compliance with specification requirements if a failure is suspected, or as an aid to predict the likely physical characteristics of the concrete in question.
The test is generally conducted chemically. Wherever possible representative samples of the cement and aggregate used in making the concrete should be obtained and chemical analyses carried out on them in a similar manner for the concrete analytical sample.
The total chloride content of concrete containing steel reinforcement is usually designed to be as low as possible to avoid early onset of corrosion of the reinforcement.
The test can be conducted in a variety of chemical means, from approximate dipstick measures through to potentiometer methods. The usual method is by titration.
This test covers the determination of the electrical conductance of concrete to provide a rapid indication of its resistance to the penetration of chloride ions. The test method is applicable to types of concrete where correlations have been established with this procedure and long-term chloride ponding procedures.
This test is used to determine the depth to which chloride ions can ingress into concrete over a period of time in standard conditions. It can be used to assess a concrete for its resistance to chloride attack and thus protection of the reinforcement from corrosion.
Samples cast in a standard manner have one face continually in contact with a chloride saturated solution for ninety days. After this time, specimens are extracted in increasing depth from the face and the chloride content of each specimen is measured.
This test is used to determine the compressive strength of a concrete core, which has usually been extracted from an existing structure. The value of compressive strength can then be used in conjunction with other measured properties to assess the condition of the concrete.
Using a masonry saw, the core is first trimmed to the correct test length, which varies upon the standard being adopted. Following trimming, the core will have its ends either ground perfectly flat, or be capped in a material to produce a smooth bearing surface. After the prescribed curing has taken place, the specimen is then crushed to failure noting the maximum load achieved. From the values of load and dimensions, the compressive strength of the core can be calculated.
Often, existing concrete structures will need to examined and tested to ensure the concrete remains of adequate strength and durability. Extraction of concrete cores, achieved by rotary drilling using a diamond tipped hollow barrel, serve as a means of taking a sample of concrete which can then be used to determine various physical properties, but most commonly compressive strength.
Cores can generally be extracted from wherever access allows, and would include floor slabs, walls and columns. 10cm diameter cores, generally afford the minimum diameter required for a representative sample and require less reinstatement than larger diameter cores.
Often, existing concrete structures will need to examined and tested to ensure the concrete remains of adequate strength and durability. Extraction of concrete cores, achieved by rotary drilling using a diamond tipped hollow barrel, serve as a means of taking a sample of concrete which can then be used to determine various physical properties, but most commonly compressive strength.
Cores can generally be extracted from wherever access allows, and would include floor slabs, walls and columns. 15cm diameter cores will generally give more representative samples than smaller diameters but require more reinstatement.
This test is used to determine the compressive strength of a concrete cube, which has usually been made from fresh concrete cast in a standard test mould. The value of compressive strength can then be used to assess whether the batch that the concrete cube represents meets the required compressive strength.
Following cube manufacture and curing, which should both be closely controlled, the cube is crushed at a stated constant speed until it can sustain no further increase in load. The strength is then derived by calculation using the maximum load and cube dimensions.
Often, existing concrete structures will need to examined and tested to ensure the concrete remains of adequate strength and durability. Over time concrete surfaces react with the carbon dioxide in air, which then carbonates the concrete, reducing its passivity and thus protection of the reinforcement from corrosion.
Values of drying shrinkage and wetting expansion of concrete are often useful to measure at the time of mix design trials to ensure the concrete will exhibit values that are within normal ranges for concrete.
The test consists of making a number of prisms of the concrete of known exact length, then either subjecting them to a drying or wetting environment. Any change is length over time is then recorded.
Although generally not such an important property of concrete than compressive strength, tensile strength values are often important to know when the concrete may be used free of reinforcement and may be subjected to some tensile force.
The test method essentially involves applying a load at the centre of a beam of concrete supported at its ends. The load required to break the specimen is then recorded.
Often, existing concrete structures will need to examined and tested to ensure the concrete remains of adequate strength and durability.
A rapid method of assessing whether there may be any delamination of the concrete surface is to conduct a hammer sounding. This involves striking the concrete surface and listening for a noise, distinctive to the trained operator of delamination.
Porosity of concrete is an important factor is classifying its durability. Generally, concrete of a low porosity will afford better protection to reinforcement within it than concrete of high porosity.
Porosity can be measured by vacuum saturation of a concrete specimen, measuring its weight gain and expressing this as a percentage of the mass of the sample.
Cores can generally be extracted from wherever access allows, and would include floor slabs, walls and columns. 10cm diameter cores, generally afford the minimum diameter required for a representative sample and require less reinstatement than larger diameter cores.
Often, existing concrete structures will need to examined and tested to ensure the concrete remains of adequate strength and durability.
Rebound hammer surveys can be conducted to provide a rough estimate of concrete strength, where it is not possible to determine this by more accurate means such as core extraction and testing.
The test involves using a special rebound hammer, which measures the recoil of a piston against the concrete surface when a standard force is applied. This recoil can then be correlated approximately to concrete strength.
Often, existing concrete structures will need to examined and tested to ensure the concrete remains of adequate strength and durability.
Measurement of the velocity of ultrasonic pulses of longitudinal vibrations passing through concrete achieved using special portable apparatus, may be used in applications such as: the determination of the uniformity of concrete or the detection and approximate extent of cracks, voids and other defects.
It can also be used when pulse velocity and strength are correlated to provide a measure of concrete quality.
Often, existing concrete structures will need to examined and tested to ensure the concrete remains of adequate strength and durability.
Measurement of the velocity of ultrasonic pulses of longitudinal vibrations passing through concrete achieved using special portable apparatus, may be used in applications such as: the determination of the uniformity of concrete or the detection and approximate extent of cracks, voids and other defects.
It can also be used when pulse velocity and strength are correlated to provide a measure of concrete quality.
Water absorption of concrete is an important factor is classifying its durability. Generally, concrete of low water absorption will afford better protection to reinforcement within it, than concrete of high water absorption.
Water absorption can be measured by soaking concrete specimens, measuring their weight gain and then expressing this as a percentage of the mass of the sample..
Water penetration of concrete is an important factor is classifying its durability. Generally, concrete of a low water penetration will afford better protection to reinforcement within it, than concrete of high water penetration.
Water penetration can be measured by applying water at a known pressure against one side of a cubic specimen. After the prescribed time, the actual depth to which the water has penetrated the cube face can be measured by splitting the cube and measuring the ingress with a rule.