Testing of Hardened Concrete & Cement Replacements
Most of the testing of hardened concrete is carried out according to the methods in BS1881:124:1988 which is a revision of BS1881: Part 6:1971. The methods which are covered in the standard are:
Sampling and Sample Preparation
Including oven dried density by BS1881: Part 114
Cement and aggregate content
Cement content is determined by soluble silica and calcium oxide methods. If the aggregate was limestone the result from soluble silica method is applied. The results are considerably more accurate if samples of the mix ingredients are available.
Original Water Content
This is calculated from the capillary porosity of the concrete and the water bound in the hydrated compounds of the cement. The water/cement ration can be calculated from the original water content and cement content.
Ordinary Portland Cement and High Alumina Cement are easily identified, together with the presence of PFA and GGBFS, SRPC can sometimes be distinguished from OPC by a microscopic method although this may be unreliable.
Aggregates can be identified by X-ray diffraction and petrographic analysis.
With hardened concrete, generally it is only possible to grade aggregates which are insoluble in hydrochloric acid.
Air Entrainment can be identified by a microscopic method.
Compressive Strength is determined to BS1881.
UK Analytical has particular expertise in the use of pulverised fuel ash (PFA). Tests include:
PFA to BS3892 part 1 for moisture content, loss on ignition, sieve residue, total SO3 and MgO. Soluble iconic constituents also to BS methods. Major constituents of PFA can be measured quantitatively. Percentage PFA in hardened concrete can also be determined to a similar accuracy as BS1881 cement content. The percentage glass content can be determined in a similar way to slag.
Ground granulated blast furnace slag (GGBFS) can be tested for use with Portland cement to BS6699: 1986, tests include:
- Glass content by X-ray diffraction
- Glass content by optical microscopy
- Fineness (specific surface area)
- Insoluble residue by BS4550
- Loss on ignition
- Moisture content
- Sulphur (total)
- Suplhur (sulphide)
- Chemical modulus