Landscape & Urban Design Issue 55 2022 | Page 47

CONCRETE & STONEWORK
bedding mortar for the laying course as described in BS 7533 part 101 , PS ECO bonding mortar , required for bound system B as per BS 7533 part 101 & FJM ECO , flowable jointing mortar or slurry grout as per BS 7533 part 101 .
GGBS is a waste product generated in huge quantities from the steel industries through the manufacture of Iron . Iron ore , coke and limestone are fed into the furnace , the resulting molten slag floats above the molten iron at a temperature of about 1500 ° C to 1600 ° C . After the molten iron is tapped off , the remaining molten slag , which consists of mainly siliceous and
aluminous residue is then waterquenched rapidly , resulting in the formation of a glassy granulate . This glassy granulate is dried and ground to the required size , which is known as GGBS . The partial replacement of OPC in concrete by GGBS , not only provides a saving on CO2 production but also facilitates environmentally friendly disposal of the waste slag .
CO2 savings that can be made through the replacement of OPC with GGBS are impressive . E . g ., the carbon footprint of Ordinary Portland Cement ( CEM II ) is 0.803 tonnes CO2 / tonne ( based on CEMbureau EPD for CEMIIs and National Cement data for
EPA license ), whereas the carbon footprint for slag ( GGBS ) is 25 x smaller at 0.032 tonnes CO2 / tonne ( based on Ecocem Third Party verified EPD ). If a percentage of OPC is replaced with GGBS , we can use the average CO2 generated per mile emitted by a car ( 0.00031 tonnes , ICCT EU Pocketbook 2014 ) or the number of trees growing for ten years absorbing 1 tonne of CO2 ( 25 trees ) to contextualise the CO2 emissions saved e . g ., if 1 tonne of product containing 25 % OPC was produced and 20 % of the OPC is replaced with GGBS this would be the same as 1 tree growing for ten years or 124 miles not driven .
Accrington Town Centre Photograph courtesy of Hardscape , hardscape . co . uk
Pottingers Entry , Belfast Photograph courtesy of Hardscape , hardscape . co . uk
Victoria Square , Belfast Photograph courtesy of Hardscape , hardscape . co . uk
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