74 research outputs found
Comparative Study of Superabsorbent Polymers and Pre‐soaked Pumice as Internal Curing Agents in Rice Husk Ash Based High‐Performance Concrete
Utilisation of superabsorbent polymers (SAP) and pre‐soaked lightweight aggregates (LWA) as internal
curing (IC) agents for the mitigation of autogenous shrinkage and micro‐cracking of high strength/highperformance
concrete (HSC/HPC) have been well researched and documented in literature. Rice husk
ash (RHA) on the other hand has been adjudged to be of good pozzolanic activity and a possible
alternative to silica fume (SF) in low water/binder (W/B) concrete production. An experimental
comparative study was conducted in the current work to assess the effectiveness of the two known ICagents
on rice husk ash (RHA) based HPC. HPC mixtures of fc,cube28=60 MPa minimum target strength
produced and internally cured with 0.3% content of SAP by weight of binder (bwob) and varied content
of pre‐soaked pumice (5 to 10% in steps of 2.5%) by weight of coarse aggregate (bwocg) were cast using
100 mm cubes samples. Thereafter, the samples were cured for 7, 14, 28 and 56 days by water
immersion before subjecting them to compressive strength test. The results showed 0.2% bwob SAP
HPC (SHPC1) to be the best performed internally cured HPC at the early ages with similar long‐term
strength values as 5 and 7.5% bwocg saturated pumiced HPC (PHPC1&2). The study thereby
recommends SAP content of 0.2% bwob and saturated pumice content up to 7.5% bwocg for use as ICagent
in HPC
Life cycle greenhouse gas emissions of blended cement concrete including carbonation and durability
The final publication is available at Springer via http://dx.doi.org/10.1007/s11367-013-0614-0Purpose Blended cements use waste products to replace
Portland cement, the main contributor to CO2 emissions in
concrete manufacture. Using blended cements reduces the
embodied greenhouse gas emissions; however, little attention
has been paid to the reduction in CO2 capture (carbonation)
and durability. The aim of this study is to determine if the
reduction in production emissions of blended cements compensates
for the reduced durability and CO2 capture.
Methods This study evaluates CO2 emissions and CO2 capture
for a reinforced concrete column during its service life
and after demolition and reuse as gravel filling material.
Concrete depletion, due to carbonation and the unavoidable
steel embedded corrosion, is studied, as this process consequently
ends the concrete service life. Carbonation deepens
progressively during service life and captures CO2 even after
demolition due to the greater exposed surface area. In this
study, results are presented as a function of cement replaced
by fly ash (FA) and blast furnace slag (BFS).
Results and discussion Concrete made with Portland cement,
FA (35%FA), and BFS blended cements (80%BFS) captures
47, 41, and 20 % of CO2 emissions, respectively. The service
life of blended cements with high amounts of cement replacement,
like CEM III/A (50 % BFS), CEM III/B (80 % BFS),
and CEMII/B-V (35%FA), was about 10%shorter, given the
higher carbonation rate coefficient. Compared to Portland
cement and despite the reduced CO2 capture and service life,
CEM III/B emitted 20 % less CO2 per year.
Conclusions To obtain reliable results in a life cycle assessment,
it is crucial to consider carbonation during use and
after demolition. Replacing Portland cement with FA, instead
of BFS, leads to a lower material emission factor, since
FA needs less processing after being collected, and transport
distances are usually shorter. However, greater reductions
were achieved using BFS, since a larger amount of cement
can be replaced. Blended cements emit less CO2 per year
during the life cycle of a structure, although a high cement
replacement reduces the service life notably. If the
demolished concrete is crushed and recycled as gravel filling
material, carbonation can cut CO2 emissions by half. A case
study is presented in this paper demonstrating how the results
may be utilized.This research was financially supported by the Spanish Ministry of Science and Innovation (research project BIA2011-23602). The authors thank the anonymous reviewers for their constructive comments and useful suggestions. The authors are also grateful for the thorough revision of the manuscript by Dr. Debra Westall.García Segura, T.; Yepes Piqueras, V.; Alcalá González, J. (2014). Life cycle greenhouse gas emissions of blended cement concrete including carbonation and durability. International Journal of Life Cycle Assessment. 19(1):3-12. https://doi.org/10.1007/s11367-013-0614-0S312191Aïtcin PC (2000) Cements of yesterday and today: concrete of tomorrow. Cem Concr Res 30(9):1349–1359Angst U, Elsener B, Larsen C (2009) Critical chloride content in reinforced concrete—a review. Cement Concr Res 39(12):1122–1138Berge B (2000) The ecology of building materials. 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