Pulverised Fuel Ash Concrete for Mass Fill & Foundations
CEM IV cement contains 21-55% pulverised fuel ash (PFA) providing low heat of hydration ideal for mass concrete foundations, dams, and thick sections where thermal cracking presents significant risk. BS EN 197-1 CEM IV/B-V specification permits up to 55% PFA replacement reducing embodied carbon by 40-60% versus CEM I Portland cement.
Slower strength gain requires extended curing periods achieving design strength at 56-90 days versus 28 days for ordinary Portland cement mixes. Excellent sulfate resistance suits aggressive ground conditions including sulfate Class DS-3 and chemical Class XA3 exposure environments common in reclaimed industrial sites.
Typical C25/30 CEM IV concrete uses 280kg/m³ CEM IV cementitious content with 45% PFA replacement yielding 154kg Portland clinker and 126kg PFA. Water/cement ratio limited to 0.50 maximum ensuring adequate durability while maintaining workability through PFA particle fineness effects.
Extended setting time 4-8 hours requires temperature control above 5°C during placement and 7-day minimum moist curing period. Pumpable consistency maintained through S3 slump class with extended workability suitable for large continuous pours exceeding 100m³ daily capacity.
Resources: BS EN 197-1, BS 8500, concrete supplier technical data
Mass foundations benefit from 20°C lower peak temperature preventing thermal cracking. Strip footings in sulfate-bearing clay soils achieve DC-2z durability without sulfate-resisting cement premium. Agricultural slurry tanks utilise chemical resistance properties extending service life significantly.
7-day strength typically 50-60% of 28-day target increasing to 110% at 90 days due to continued PFA pozzolanic reaction. Early-age loading restricted to 65% design capacity at 7 days, 85% at 28 days ensuring structural safety during construction phases.
45% PFA replacement reduces CO₂ emissions from 950kg/m³ (CEM I) to 480kg/m³ representing 50% carbon saving. Material cost premium 5-10% versus CEM I offset through sulfate resistance eliminating specialist cement requirements. Availability concentrated around power station regions with bulk transport logistics.
| CEM IV Type | PFA Content | CO₂/m³ | Strength Gain |
|---|---|---|---|
| CEM IV/A-V | 21-35% | 720kg | 28 days |
| CEM IV/B-V | 36-55% | 480kg | 56 days |
| C25/30 Typical | 45% PFA | 500kg | DC-2z sulfate |
| Mass Foundation | 50% PFA | 20°C peak | Low heat |
45% PFA replacement cuts embodied COâ‚‚ from 950kg to 480kg per cubic metre concrete.
20°C peak temperature versus 45°C CEM I preventing thermal cracking in thick sections.
Exceeds DC-2z requirements without sulfate-resisting cement cost premium.
Extended curing achieves 110% target strength through pozzolanic reaction.
5-10% premium versus CEM I offset by durability advantages.
CEM IV/B-V specification with verified pozzolanic performance data.
Portland-pozzolana cement with 21-55% PFA providing low heat and sulfate resistance.
50-60% at 7 days, 85% at 28 days, 110% at 90 days due to pozzolanic reaction.
Mass foundations, strip footings in sulfate soils, agricultural tanks, thick slabs.
45% PFA reduces emissions 50% versus CEM I Portland cement mixes.
5°C continuous with 7-day moist curing protection essential.
S3 slump maintained 2-3 hours with excellent pumpability through fine PFA particles.
5-10% premium offset by sulfate resistance eliminating specialist cement costs.
Concentrated around former power stations with bulk logistics to nationwide plants.
Resources: BS EN 197-1 specifications, concrete suppliers, technical data sheets