Durability Properties and Microstructure of Ground Granulated Blast Furnace Slag Cement Concrete
© The Author(s) 2014
Received: 29 April 2013
Accepted: 4 December 2013
Published: 20 May 2014
Ground granulated blast-furnace slag (GGBS) is a green construction material used to produce durable concrete. The secondary pozzolanic reactions can result in reduced pore connectivity; therefore, replacing partial amount of Portland cement (PC) with GGBS can significantly reduce the risk of sulfate attack, alkali–silica reactions and chloride penetration. However, it may also reduce the concrete resistance against carbonation. Due to the time consuming process of concrete carbonation, many researchers have used accelerated carbonation test to shorten the experimental time. However, there are always some uncertainties in the accelerated carbonation test results. Most importantly, the moisture content and moisture profile of the concrete before the carbonation test can significantly affect the test results. In this work, more than 200 samples with various water–cementitious material ratios and various replacement percentages of GGBS were cast. The compressive strength, electrical resistivity, chloride permeability and carbonation tests were conducted. The moisture loss and microstructure of concrete were studied. The partial replacement of PC with GGBS produced considerable improvement on various properties of concrete.
Manufacturing Portland cement (PC) is a major contributor of greenhouse gases, responsible for about 5 % of all global carbon dioxide emissions (Habert and Roussel 2009). In comparison, the production of ground granulated blast-furnace slag (GGBS) requires less than a fifth of the energy and produces less than a tenth of the carbon dioxide emissions. It is well known that blast furnace slag cement (BFSC) has been manufactured by integrating GGBS with cement clinker or by separate grinding (Wang et al. 2005). For a long period of time, the application of GGBS was limited to the production of BFSC. Due to its less grindability, the surface area of the produced BFSC was even lower than that of commercial PC and its reactivity was limited. With advancement in technology, finer GGBS (particle size less than 10 μm) with increased reactivity was produced. The secondary pozzolanic reactions can result in reduced pore connectivity in the concrete. Therefore, partial replacement of PC with GGBS can significantly reduce the risk of sulfate attack, alkali–silica reactions and chloride penetration and increase compressive strength (Güneyisi and Gesoğlu 2008; Hadj-Sadok et al. 2010; Nazari and Riahi 2011; Shi et al. 2011, 2012; Teng et al. 2013). However, it may reduce the resistance of the concrete against carbonation (Harrison et al. 2012; Shi et al. 2009; Jia et al. 2011).
Concrete carbonation is one of the most important phenomena affecting the durability of concrete. Concrete carbonation has been studied extensively over the last few decades. However, due to the time consuming process of carbonation, many researchers have used accelerated carbonation test to shorten the experimental time. Considering the complex process of carbonation and the number of parameters involved, there are always some uncertainties in the accelerated carbonation test results. Most importantly, the moisture content and moisture profile of the concrete before the carbonation test can significantly affect the test results. The CO2 from the environment will dissolve in the pore solution through the partially filled pore system and will react with the cement hydration products. If the concrete is fully saturated, carbonation will be slow (Lagerblad 2005). Based on the quality of concrete and the environmental conditions, concrete will achieve equilibrium moisture profile status after several months (Sabet and Jong 2006). To shorten this time, various preconditioning techniques were employed before the carbonation test. Oven drying is one of the most popular methods. However, the high temperature drying can damage the pore structure of concrete (Galle 2001). Partial replacement of PC with supplementary cementitious materials (SCM) is known to reduce the resistance against carbonation due to consumption of calcium hydroxide during pozzolanic reactions. On the other hand, the finer pore structure and lower permeability due to SCM replacement results in higher degree of internal saturation which may slow down the carbonation rate. This improvement may diminish as a result of artificial preconditioning which could damage the pore structure and lower the degree of internal saturation below the natural equilibrium for blended cement concrete. Therefore, the increased carbonation rate measured in accelerated carbonation test may not be the correct natural carbonation rate of blended cement concrete. Jia et al. (2011) also suggested that the accelerated carbonation method sometimes may ‘enlarge’ the influence of the mineral admixture content and change the dynamics of concrete in carbonation.
In this work, more than 200 samples with various water–cementitious material ratios (0.4, 0.5 and 0.6) and various replacement percentages of GGBS were cast. The compressive strength, electrical resistivity, chloride permeability and carbonation tests were conducted during 4 years of experimental study. The moisture loss was recorded by gravimetric technique and the microstructure of the concrete was investigated using the mercury intrusion porosimetry (MIP). The results showed that partial replacement of PC with GGBS contributed considerable improvement on various properties of concrete.
2 Experimental Work
Physical and chemical characteristics of PC and GGBS.
Portland cement (II)
Blaine surface area (m2/kg)
BET surface area (m2/kg)
Mean particle diameter (μm)
Chemical analysis (%)
Concrete mix proportions.
Total cementitious materials (kg/m3)
The cube compressive strength test was completed using a 3,000 kN compression machine according to BS EN 12390-3 (2009). The mercury intrusion porosimeter 9400 Series was used to study the microstruture of concrete. The MIP gradually forces mercury into the pores of concrete from evacuated condition (50 μmHg pressure) to high pressure of about 60,000 Psia (Ji and Jong 2003). The MIP results were used to study the effect of GGBS replacement and preconditioning on the pore structure of concrete. The gravimetric weight loss of the concrete was studied in controlled drying condition at relative humidity of 75 % and temperature of around 28 °C. The drying rate of concrete after oven drying and re-wetting was also studied to demonstrate the effect of oven drying at 105 °C on microstructure of concrete.
3 Results and Discussions
Increased slump and fluidity was measured with the increase in GGBS replacement percentage. For water–cementitious material ratio (w/c) = 0.5 and aggregate/cementitious material ratio (a/c) = 3, the slump was increased by 20, 35 and 55 % for 10, 30 and 50 % GGBS replacement, respectively. Similar improvement was reported elsewhere (Gao et al. 2005) for the partial replacement of PC with GGBS.
3.1 Mechanical Properties
3.2 Microstructure of Concrete
3.3 Gravimetric Weight Loss and Pore Structure of Concrete
3.4 Chloride Permeability and Electrical Restively Results
Chloride ion penetrability based on charge passed (ASTM C1202-10 2010).
Charge passed (C)
Chloride ion permeability
Relationship between concrete resistivity and corrosion rate (ACI 222R-01 2001).
Resistivity (kΩ cm)
Low to moderate
3.5 Carbonation Results
This experiment showed that partial replacement of PC with GGBS improved the pore structure of concrete. The electrical resistivity of the concrete was increased and the total coulombs passed during rapid chloride permeability test were significantly reduced. The rate of carbonation for the samples with 30 and 50 % GGBS replacement increased, however longer period of water curing for GGBS blended cement concrete reduced the carbonation rate and reduce the concern of increased carbonation rate. On top of ecological reasons such as reduced CO2 foot print and consumption of GGBS (a waste by product of iron production), the GGBS is a viable pozzolanic material for everyday construction purposes considering the improvement in fresh concrete properties, mechanical properties and durability properties.
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