CRL Surveys assessments follow the guidance given in Concrete Society Technical Report 68.
Stage 1 Preliminary Inspection
A Stage 1 Preliminary Inspection should be undertaken by appropriate specialists, including a Structural Engineer experienced with fire damaged structures, with all necessary temporary works (propping) done prior to the following.
Stage 2 Assessment of Damage (Essentially Non-Destructive) We will undertake a detailed, close-quarters tactile visual inspection and hammer test survey, as described elsewhere, but additionally focussing on Macroscopical Changes / Effects in ‘2D’. The concrete surfaces and associated debris will be assessed for evidence of severity of damage. This will include an assessment of discolouration, sooting and invasive damage to surface finishes, in addition to discolouration of the concrete surface zones. Concrete Society Technical Report 68 gives guidance on potential evidence that may be available for the assessment of the temperature attained by the fire and the severity of the exposure of the concrete. The results of the visual inspection and hammer testing will be used to prepare record drawings, onto which the condition of the surfaces will be assessed and classified, in general accordance with the guidance provided in Table 7 and Figure 20 of Concrete Society Technical Report 68. In addition, wherever possible, the depth and extent of surface loss due to spalling / delamination will be recorded.
Stage 3 Testing and Detailed Assessment (Partially Destructive)
NB: Unless otherwise requested we do not normally undertake thermal modelling or dimensional surveys for the assessment of deflections / lateral movements.
Macroscopical Changes / Effects at Depth:- The results of the Stage 2 Assessment of damage, and in particular the drawings prepared, will be used to focus further investigations. In a limited number of representative locations, i.e. representative of the various elements and damage classifications identified (including, for reference un-damaged, ‘as-built’ concrete), nominal 30mm diameter concrete core samples will be prepared using a rigidly mounted rotary drill fitted with a diamond-tipped core bit. The core samples will each be subjected to a ‘simple’ visual inspection, with record photographs prepared, to show an overview of each core and any salient features. A representative selection of the cores will then be submitted to a UKAS Accredited laboratory for preparation and detailed petrographical analysis in accordance with the procedures described within ASTM C856. The concrete will be analysed for general composition and condition, with attention also focussed on any features potentially indicative or suggestive of exposure to elevated temperatures. The results of these investigations would be used to resolve in more detail the extent of concrete repairs required. Residual Strength of Concrete:- The residual strength of the concrete can be assessed by either the determination of rebound number in accordance with BS EN 12504 or by the testing of additional core samples in accordance with BS EN 12504: Part 1: 2000, with testing for saturated density in accordance with BS 1881: Part 114: 1983. Residual Strength of Reinforcement:- Selected, representative samples of the reinforcement will be cut from the structure/s concerned and submitted to a UKAS Accredited Laboratory, for preparation and testing for tensile strength in general accordance with the procedures described within BS EN 10002. In summary, nominal 600mm lengths of reinforcement would be disc-cut from the structure, subjected to testing at ambient temperature and the results then compared with the values given variously within the age related issues of BS 4449. Stage 4 Design of Repairs to Structural Elements
NB: We generally evaluate the repairs required, in terms of probable form and approximate size, so that approximate quantities may be estimated.
Assessment of Concrete Patch-Repairs Required:- Visual inspection and hammer testing, as described elsewhere will be carried out with due regard to guidance provided within BS EN 1504 and other industry guidance documents. The Underlying Condition of the Concrete:-
NB: As the intention of our investigations will be to enable concrete repairs, assuming that the damage to the structure/s is repairable, in our opinion, an assessment should include an assessment of underlying concrete condition, so that the concrete repairs strategy can be formulated with optimum life-to-first-maintenance.
We would therefore recommend assessments of; Depths of cover to the reinforcement, screening drilled dust samples for Chloride and in-situ testing for depths of carbonation