Page 4 - Open-Access-Sep-2019

TECHNICAL PAPER

EffEcts of scMs

AnD nAno- AnD

UltrAfInE-MAtErIAls

on MEchAnIcAl

ProPErtIEs AnD

cArbon footPrInt of

rEcyclED AggrEgAtE

concrEtEs FAIz uDDIn AHMED sHAIkH

Abstract slag concretes containing 50% RCA. The addition of nano silica
and ultrafine fly ash also improved the compressive strength of
This paper presents the effects of supplementary cementitious recycled aggregate concrete. Similar results are also observed
materials (SCMs) (Fly ash, slag and silica fume) and emerging in the case of indirect tensile strength. The carbon footprint of
nano- and ultrafine-materials (nano silica and ultrafine fly ash) recycled aggregate concrete is slightly higher than the control
on mechanical properties of concrete containing 50% recycled concrete. However, the addition of SCMs reduced the carbon
coarse aggregate (RCA) as partial replacement of natural coarse footprint significantly.
aggregate. The RCA are mixed construction and demolition
(C&D) waste consisted of concrete, masonry and other materials. Keywords: Aggregate, Concrete, Construction, CO 2 emission,
In the first part, the effects of 50% slag or 50% fly ash as partial Demolition, Fly ash, Nano silica, Recycled, Silica fume, Slag,
replacement of ordinary Portland cement (OPC) in concrete Ultrafine fly ash, Waste.
containing 50% RCA is evaluated, while in second part the
effects of 5, 10 and 15% silica fume on above recycled aggregate
concrete containing 50% slag or 50% fly ash are evaluated. In 1. introDuCtion
third part, the effects of 2% nano silica (NS) and 10% ultrafine fly Global demand for concrete, as the main construction material,
ash (UFFA) on concrete containing 50% RCA are evaluated. The is increasing every year. As a result the demand for cement and
above results are compared with control concrete containing aggregates is unavoidable. The increasing use of cement and
100% and 50% natural coarse aggregate. Water-to-binder ratios aggregates significantly affects the environmental friendliness
of all concrete are kept constant, however, superplasticizer is of concrete as the raw materials for cement and aggregates
added in the mixes containing silica fume, nano silica and ultra are source from nature and the manufacturing of Portland
fine fly ash to improve the workability. The compressive and cement clinker releases about 5-7% CO 2 into atmosphere
indirect tensile strengths of all concrete are measured at 7, 28, (Limbachiya et al., 2014). These cause significant impact to
56 and 91 days. The results show that due to addition of 50% natural ecosystem and the global climate change. To address
RCA the compressive strength of concrete at all ages is reduced these issues researchers around the world are researching
significantly compared to control concrete containing 100% on new types of concretes containing various supplementary
natural coarse aggregates. The addition of high volume fly ash cementitious materials (SCM) as partial replacement of cement
and slag further reduced the compressive strength of recycled and construction and demolition (C&D) wastes as partial
aggregate concrete at all ages, where high volume fly ash shows replacement of natural aggregates in concrete. Typically, the use
more reduction in compressive strength than high volume of SCM e.g. 20–30% fly ash, 40-50% slag and 5–10% silica fume
slag. The addition of silica fume is, however, recovered the as partial replacement of Ordinary Portland Cement (OPC) and
compressive strength reduction of both high volume fly ash and 20–30% replacement of natural aggregates by recycled concrete

The IndIan ConCreTe Journal | SepTember 2019 55