In most cases inaccurate record keeping of structural plans means that there are no accurate evidence of structural elements in the concrete. We conduct Concrete Structural Inspections using GPR (Concrete X-Ray / Concrete Scanning) to provide accurate information including;
- Rebar Spacing, Diameter and Depth as well as Post Tension Cable Ducts
- Voids Beneath and Inside Slabs as well as Block Walls
- Depth of Slab
- Ultrasonic Thickness Testing of Metals
- Ultrasonic Pulse Velocity Testing (UPV)
- Surface Hardness Testing (By Rebound-Schmidt Hammer)
- The location of Structural Beams
- Verification / breakout Work (Including reinstatement with high strength, low shrinkage structural mortar and waterproofing membranes if required)
- Core Drilling Services
- Laboratory Testing of Samples
We specialise in providing complete and accurate surveys that incorporates the core drilling or taking of samples for external NATA endorsed laboratory testing for;
- Compressive Strength
- Chemical Analysis
Carbonation / Chemical Testing
Carbonation of the concrete occurs when the carbon dioxide in the atmosphere in the presence of moisture reacts with the hydrated cement minerals to produce carbonates, eg; calcium carbonate. The carbonation Process is also depassivation. Carbonation penetrates below the exposed surface of concrete extremely slowly.
The time required for carbonation can be estimated knowing the concrete grade and permeability.
The significance of carbonation is that the usual protection of the reinforcement generally present in concrete due to the alkaline conditions caused by hydrated cement paste is neutralised by carbonation.
Thus if the entire concrete cover over the reinforcement is carbonated, corrosion would occur if Moisture and oxygen could reach the reinforcement.
Carbonation depth is assessed using a solution of phenolphthalein indicator that appears pink in contact with alkaline concrete with ph values of 9.0 and colourless at lower levels of ph.
The test is most commonly carried out by spraying the indicator on freshly exposed surfaces of concrete broken from the structure or split cores.
Compressive Strength Testing
This method is for obtaining and testing the strength of drilled cores. The cores are extracted from hardened in-place concrete primarlily to ascertain the concrete strength. They can also be used to verify compliance with construction dimensional tolerances, condition evaluation of structures, forensic evaluation using petrography and chemical methods, estimating the composition of concrete & density and voids analysis.
Ultrasonic Pulse Velocity Testing (UPV)
When an ultrasonic pulse travelling through concrete meets a concrete-air interface, there is a negligible transmission of energy across this interface. Thus, any air-filled crack or void lying immediatley between the two transducers will obstruct the direct ultrasonic beam when the projected length of the void is greater than the width of the transducers and the wavelength of sound used. When this happens, the first pulse to arrive at the recieving transducer will have been diffracted around the periphery of the defect and the transit time will be longer than in a similair concrete with no defect.
An estimate of crack depth visible at the surface may be obtained by measuring the transit times across the crack for two different transducers placed on the surface.
Half-Cell Potential Testing (Corrosion Mapping)
Corrosion of reinforcing steel is an electro-chemical process and the behaviour of the steel can be charactorised by measuring its half-cell potential. The greater the potential the higher the risk that corrosion is taking place. An electrode forms one half of the cell and the reinforceing steel in the concrete the other. The preferred reference electrode for site use is silver/silver chloride in potassium chloride solution although the copper/copper sulphate electrode is still widely used.
The survey procedure is firstly to locate the reinforcment and etermine the bar spacing using high frequency impulse radar (concrete scanning). A suitable connection to the reinforcement is made on both sides of the test area. It is neccassry to check that the reinforcment is continuous by measuring the resistance between two widely seperated points.
The reinforcement is connected to the half cell via the corromap unit. Readings of half-cell potential are taken over a regular grid of points to give a potential map of the area.
Contour lines may be plotted between points of equal potential to indicate those areas that have the greatest risk of corrosion. Locally exposing and inspecting the reinforcement in areas where both high and low risks of corrosion are indicated can be used to approximately calibrate the potential readings for the structure with respect to its present corrosion and the need for further investigation or repair.