Posted: Mon Nov 19, 2012 8:50 pm
LLL - not sure what you mean by "pavemix". Some volumetric and ready mixed concrete companies use proprietary names to describe some of their concretes - Cemex being one. If it's a C30 (technically it should be described as C25/30) with fibres, it should be fine. BS 8500 specifies a GEN 2 (C16/20) and GEN 3 (C16/20) for house and garage floors respectively that are unreinforced, i.e. contain no embedded metal. For reinforced floors, the minimum grade should be C25/30 unless something higher is specified by design.
To be clear, you only need air entrainment if the concrete is an external slab exposed to the elements, e.g. house drive, car park etc. However, if you do need it, the possible problem with a volumetric truck is the very short mixing time - this may not be enough to entrain the volume of air required to provide resistance to frost damage of the hardened concrete. The only certain method is to carry out an air test on site using a special pressure meter - generally only available on request - if you're lucky!! QSRMC and BSI certified companies (see below) have to test for air content routinely to ensure it falls within BS limits. If the air content is excessively high, it can be just as bad as having no air entrainment at all.
For info, with regard to the volumetrics (and some of the smaller ready mixed concrete companies), they can only supply designated (not to be confused with designed) concretes prefixed with GEN, RC, PAV and FND if they are third party certified by QSRMC (Quality Scheme for Ready Mixed Concrete) or kitemarked via BSI (British Standards Institution). They are, however, entitled to supply alternative designed concretes such as C16/20, C25/30 etc. QSRMC and BSI certified companies are subject to regular visits by external assessors who check the whole quality system from start to finish.
If you are powerfloating in the winter and assuming it's ultimately an internal slab , I strongly recommend you specify a C28/35 with a minimum cement content of 330 kg/m3 CEMI (100% OPC) or a higher grade if it's industrial use. Do not use blended cemnents containing ggbs or pfa such as CIIIA or CIIB-V. Finally, most of the big powerfloat boys specifically ask us NOT to include an admixture such as a plasticiser/water reducer as they can retard the set in the winter (as can ggbs / pfa) - they don't like working till 2 or 3 am the following morning. An 8 am start is ideal as long as it's not too cold. Cover with hessian if necessary - generally not done by the big boys.
Sorry to go on a bit (as usual)!!
To be clear, you only need air entrainment if the concrete is an external slab exposed to the elements, e.g. house drive, car park etc. However, if you do need it, the possible problem with a volumetric truck is the very short mixing time - this may not be enough to entrain the volume of air required to provide resistance to frost damage of the hardened concrete. The only certain method is to carry out an air test on site using a special pressure meter - generally only available on request - if you're lucky!! QSRMC and BSI certified companies (see below) have to test for air content routinely to ensure it falls within BS limits. If the air content is excessively high, it can be just as bad as having no air entrainment at all.
For info, with regard to the volumetrics (and some of the smaller ready mixed concrete companies), they can only supply designated (not to be confused with designed) concretes prefixed with GEN, RC, PAV and FND if they are third party certified by QSRMC (Quality Scheme for Ready Mixed Concrete) or kitemarked via BSI (British Standards Institution). They are, however, entitled to supply alternative designed concretes such as C16/20, C25/30 etc. QSRMC and BSI certified companies are subject to regular visits by external assessors who check the whole quality system from start to finish.
If you are powerfloating in the winter and assuming it's ultimately an internal slab , I strongly recommend you specify a C28/35 with a minimum cement content of 330 kg/m3 CEMI (100% OPC) or a higher grade if it's industrial use. Do not use blended cemnents containing ggbs or pfa such as CIIIA or CIIB-V. Finally, most of the big powerfloat boys specifically ask us NOT to include an admixture such as a plasticiser/water reducer as they can retard the set in the winter (as can ggbs / pfa) - they don't like working till 2 or 3 am the following morning. An 8 am start is ideal as long as it's not too cold. Cover with hessian if necessary - generally not done by the big boys.
Sorry to go on a bit (as usual)!!
