RP1020: Reducing Barriers for Commercial Adaptation of Construction Materials with Low-Embodied-Carbon

_{Peer Reviewed Research Publications}

RP1020: Journal Article: Steel reinforcement corrosion in a low calcium fly ash geopolymer concrete

Geopolymer concrete (GPC) has significant potential as a more sustainable, low-embodied carbon alternative for ordinary Portland cement concrete (PCC). However; as a rather new engineering material, there are some concerns over the durability aspects of geopolymeric binders.

In this study, performance of chloride contaminated reinforced GPC specimens manufactured using low calcium fly ash is investigated by long-term monitoring of corrosion parameters such as free corrosion potential and polarization resistance. It was found that low calcium fly ash GPC can perform as well as PCC during the propagation phase of corrosion; although, some conventional reference values of corrosion parameters which are indicative of severity of the steel corrosion in PCC are not suitable for GPC. Additionally, commonly used electrochemical test methods are successfully employed to assess the degree of reinforcement corrosion in geopolymeric binders within an acceptable level of accuracy.

Read the full article here: https://doi.org/10.4028/www.scientific.net/KEM.711.943

RP1020: Journal Article: Durability performance of precast fly ash–based geopolymer concrete under atmospheric exposure conditions

This study investigates the durability of precast fly ash–based geopolymer concrete (GPC) exposed to an outdoor atmospheric environment for 8 years. Core specimens from GPC culverts are tested to determine the effect of carbonation, permeation properties, and pore-size distribution, and the durability is compared with that of ordinary portland cement (OPC) concrete from the same exposure environment. It is found that the GPC has lower carbonation resistance than OPC concrete. According to mercury intrusion porosimetry (MIP) test results, the porosity of the GPC surface increased with carbonation under field-exposed conditions, whereas no significant changes occurred between laboratory-prepared carbonated and uncarbonated GPC specimens. The GPC produced sodium-based carbonation products that are soluble in water. The surface porosity of the GPC therefore increased, and this process accelerates the carbonation in field conditions. In addition, sorptivity test results correlate well with the MIP analysis and carbonation resistance. Therefore this study reveals that the fly ash–based geopolymer concrete is more susceptible to carbonation in an atmospheric environment.

 Read the full paper here: DOI: 10.1061/(ASCE)MT.1943-5533.0002165

RP1020: Journal Article: Carbonation of a low-calcium fly ash geopolymer concrete

The carbonation resistance of a blended slag and low-calcium fly ash (FA) geopolymer concrete was investigated. The geopolymer binder studied was composed of 90% low-calcium FA and 10% ground granulated blast-furnace slag. The alkalinity of the pore solution plays a pivotal role in carbonation progression and subsequent corrosion initiation. pH profiles were measured to assess the pore solution alkalinity. Phenolphthalein indicator was used to measure the carbonation depth. X-ray diffraction (XRD) and quantification were carried out to identify and quantify the carbonation products. The obtained pH profiles illustrated a wider semi-carbonation zone in the geopolymer specimens, although the pH drop was insignificant in most cases. XRD analysis revealed that nahcolite mainly formed at 3% carbon dioxide concentration and led to a significant drop in pH values.

The results further demonstrated that 1% accelerated carbonation replicated the natural carbonation process well, with only natron identified as a carbonation product. This work contributes to the assessment of the risk of carbonation-induced reinforcement corrosion in low-calcium FA geopolymer concrete.

Read the full article here: https://doi.org/10.1680/jmacr.15.00486

RP1020: Journal Article: Durability performance of concrete structures built with low carbon construction materials

Here, we demonstrate the feasibility of industrial application of low carbon supplementary cementitious materials (i.e. geopolymer concrete) by investigating the durability performance of eight years aged reinforced geopolymer concrete structure exposed to ambient environment. The corrosion performance of reinforcement bar in concrete and permeability characteristic of cover concrete is investigated by using non-destructive techniques. The results reveal that the reinforcement in geopolymer concrete exhibits higher corrosion risk in atmospheric environment and this attributes to the deterioration of long term durability performance for geopolymer concrete.

Read the full article here: https://doi.org/10.1016/j.egypro.2016.06.130

RP1020: Journal Article: Carbonation of a blended slag-fly ash geopolymer concrete in field conditions after 8 years

In this study, the carbonation resistance of two geopolymer concretes exposed to outdoor field conditions for eight years was investigated. Core specimens were used to determine the in-situ carbonation depth, concrete porosity was assessed and the carbonation reaction products of aged concrete were identified by TGA and FT-IR analysis. Carbonation of the geopolymer concretes was compared to OPC and fly ash concretes exposed to similar conditions. The results indicated that the carbonation rate of geopolymer concrete is highly dependent on the activator components of geopolymer concrete. Type 1 geopolymer concrete, with 75% fly ash/25% GGBFS and additional Na2SiO3 activator, showed a poor resistance against carbonation compared to OPC concrete. However, the performance of Type 2 geopolymer with 70% fly ash/30% GGBFS and no additional Na2SiO3 activator, was similar to OPC concrete. In addition, water absorption, sorptivity, total porosity and differential pore size distribution analysis correlated well with the carbonation resistance. Investigation of long term durability performance of geopolymer concrete is critical for the development of standard specifications for commercial application.

This study reveals that two geopolymer concretes, with a similar mix design and compressive strength, have different carbonation behaviour. Therefore, a performance based approach is an appropriate strategy to develop standard specifications for geopolymer concrete.

Read the full article here: https://doi.org/10.1016/j.conbuildmat.2016.08.078

RP1020: Journal Article: Prediction of the steel-concrete bond strength from the compressive strength of Portland cement and geopolymer concretes

The oldest and simplest bond test, which is the standard concentric pull out test, is usually used as a comparative test for different concretes in order to assess the bond with deformed bars. In this paper, two types of concrete are considered: Ordinary Portland cement (OPC) concrete and a novel concrete technology, namely geopolymer concrete (GPC). Bond strength was investigated by conducting pull-out tests on ribbed bars with a nominal diameter of 10 mm and/or 12 mm. The specimens were tested at various ages ranging from 1 to 28 days. Compression tests were performed at all ages as well. The main objective of the extensive research program involving 260 pull-out tests was to develop empirical models correlating the steel-concrete bond strength to the mean compressive strength of concrete for both OPC and geopolymer concretes. The models developed are compared to the existing model adopted by FIP Committee.

Read the full article here: https://doi.org/10.1016/j.conbuildmat.2016.05.002

RP1020: Journal Article: Recycling of geopolymer concrete

Due to its considerably lower embodied carbon and making use of industrial by-products including fly ash and ground granulated blast-furnace slag, geopolymer concrete (GPC) is considered as a sustainable alternative to Portland cement (OPC) concrete. However, prior to granting GPC a green label and encouraging its widespread use, a number of other important possible impacts associated with this new material throughout its life cycle need to be further investigated. One of the important aspects of sustainability which has received little attention with regards to GPC is the end-of-life impact. While end-of-life strategies such as recycling and reuse have been widely investigated for conventional concrete, the applicability of such strategies to GPC has not been investigated.

This paper presents the results of an experimental study conducted to investigate the recyclability of GPC. Basic properties of recycled geopolymer aggregates (RGAs) including water absorption, density and Los Angeles abrasion loss as well as the effects of size of RGA on these properties were investigated. In addition, the effects of the different replacement ratios of coarse RGA for coarse natural aggregates on the properties of the new recycled aggregate geopolymer concrete (RAG) including compressive strength, flexural strength and modulus of elasticity were investigated. The RGA and RAG properties were compared with those of recycled OPC concrete aggregate (RCA) and recycled aggregate OPC concrete (RAC) produced under relatively similar conditions.

Read the full paper here: https://doi.org/10.1016/j.conbuildmat.2015.10.037

RP1020: Journal Article: Durability of low‑calcium fly ash based geopolymer concrete culvert in a saline environment

This study reports the investigation of the durability of a low-calcium fly ash based geopolymer concrete (GPC) mix in a saline lake environment. Core specimens from the GPC and Ordinary Portland Cement (OPC) concrete structures underwent durability assessment including in-situ carbonation, chloride and sulphate ingress, microstructural characterization and porosity analysis. It was found that the particular GPC mix design studied was more vulnerable to carbonation and the deterioration effects due to chloride and sulphate ingress in GPC were higher than OPC concrete after 6 years of exposure. According to FT-IR and XRD analysis, there was no evidence of carbonation reaction products remaining in GPC. This indicates that the carbonation products dissolved when in contact with water, which caused high porosity of the concrete surface thereby facilitating more diffusion into the concrete.

This study revealed that the development of a durable geopolymer concrete mix design for aggressive environments requires appropriate consideration of binder chemistry and preliminarily durability property testing to avoid premature deterioration.

Read the full article here: https://doi.org/10.1016/j.cemconres.2017.07.010

RP1020: Journal Article: Utilisation of steel furnace slag coarse aggregate in a low calcium fly ash geopolymer concrete

This paper evaluates the performance of steel furnace slag (SFS) coarse aggregate in blended slag and low calcium fly ash geopolymer concrete (GPC). The geopolymer binder is composed of 90% of low calcium fly ash and 10% of ground granulated blast furnace slag (GGBFS). Mechanical and physical properties, shrinkage, and detailed microstructure analysis were carried out. The results showed that geopolymer concrete with SFS aggregate offered higher compressive strength, surface resistivity and pulse velocity than that of GPC with traditional aggregate. The shrinkage results showed no expansion or swelling due to delayed calcium oxide (CaO) hydration after 320 days. No traditional porous interfacial transition zone (ITZ) was detected using scanning electron microscopy, indicating a better bond between SFS aggregate and geopolymer matrix. Energy dispersive spectroscopy results further revealed calcium (Ca) diffusion at the vicinity of ITZ. Raman spectroscopy results showed no new crystalline phase formed due to Ca diffusion. X-ray fluorescence result showed Mg diffusion from SFS aggregate towards geopolymer matrix. The incorporation of Ca and Mg into the geopolymer structure and better bond between SFS aggregate and geopolymer matrix are the most likely reasons for the higher compressive strength observed in GPC with SFS aggregate.

Read the full article here: https://doi.org/10.1016/j.cemconres.2016.09.001

RP1020: Journal Article: Chloride-induced corrosion of reinforcement in low-calcium fly ash-based geopolymer concrete

Geopolymer concrete (GPC) has significant potential as a more sustainable alternative for ordinary Portland cement concrete (PCC). However; as a rather new engineering material, there are some concerns over the durability aspects of geopolymer-based binders. In this study, the performance of chloride-contaminated reinforced GPC specimens manufactured using a blended low-calcium fly ash and slag cement is investigated by long-term monitoring of corrosion parameters such as open circuit corrosion potential, polarization resistance and Tafel slopes. The electrochemical results are validated by contrasting the electrochemical mass losses with the mass losses obtained from the gravimetric measurements. The investigated low-calcium fly ash-based GPC exhibit a comparable electrochemical performance to a similar strength PCC during the propagation phase of corrosion. Additionally, some of the conventional classifications which are commonly used to assess the severity of corrosion in Portland cement-based corroding systems might need some recalibration to be used for low-calcium fly ash-based corroding systems.

Read the full article here: https://doi.org/10.1016/j.cemconres.2016.05.012

RP1020: Journal Article: Bond strength between blended slag and Class F fly ash geopolymer concrete with steel reinforcement

In this paper, geopolymer concrete bond with both deformed and smooth reinforcing steel bars is investigated using the standard RILEM pull-out test. The geopolymer binder is composed of 85.2% of low calcium fly ash and 14.8% of ground granulated blast furnace slag (GGBFS). The tests were aimed to assess the development of the bond strength from 24 h to 28 days after casting, with different heat curing conditions. The results show that 48 h of heat curing at 80 °C is required in order to obtain similar or better performances to those of the reference 45 MPa OPC concrete. The 28-day bond strength and the overall bond stress–slip behaviour of the geopolymer concrete were similar to those previously reported for OPC-based concretes. Providing intensive heat curing, high early bond strength can be achieved showing that Class F fly ash geopolymer concrete is well suited for precast applications.

Read the full article here: https://doi.org/10.1016/j.cemconres.2015.02.016

RP1020: Journal Article: Compressive stress-strain model for low-calcium fly ash-based geopolymer and heat-cured Portland cement concrete

This research focuses on elucidating the present knowledge gaps in geopolymer concrete's engineering properties, specifically its stress-strain behaviour. Geopolymer concrete (GPC) is an emerging alternative to ordinary Portland cement concrete (OPCC), and is produced via a polycondensation reaction between aluminosilicate source materials and an alkaline solution. As a relatively new material, many engineering properties of geopolymer concrete are still undetermined. In this paper, the compressive strength, modulus of elasticity and stress-strain behaviour of ambient and heat-cured GPC and OPCC have been studied experimentally. A total of 195 geopolymer concrete cylinders and 210 Portland cement concrete cylinders were tested for the above mentioned characteristics. Based on the experimental results, constitutive models describing the complete stress–strain behaviour in uniaxial compression have been developed for the low-calcium fly ash-based geopolymer concrete and the heat-cured Portland cement concrete.

Read the full paper here: https://doi.org/10.1016/j.cemconcomp.2016.07.004

RP1020: Conference Paper: A resistivity-based approach to indicate chloride permeability of geopolymer concrete

Chloride ion penetration in concrete is one of the major causes of deterioration of reinforced concrete structures by depassivation of reinforcing bars. Since testing of the natural chloride penetration is time consuming, utilising an accelerated test method is more desirable. Surface resistivity (SR) test is increasingly being used, due to its relative speed and ease of performing combined with the non-destructive nature, to assess the permeability of concrete and its resistance to chloride ion penetration. The test has been standardised as AASHTO TP 95 which consists of measuring the resistivity of water-saturated concrete cylinders using a four-pin Wenner probe array. This paper present the results of an experimental investigation on the surface resistivity (SR) of a low-calcium fly ash-based geopolymer concrete (GPC). SR test results show that the resistivity of GPC samples are very low, this does not necessarily mean that they are having a high level of chloride penetrability since the AASHTO TP 95 limits are only applicable for conventional OPC concrete and not for the GPC. In case of geopolymer concrete, there are a large amount of mobile metallic ions such as Na + in the pore solution which could probably affect the resistivity test measurements.

A further study is required to directly measure the chloride permeability of the GPC such as natural diffusion or ponding test to be able to properly correlate the surface resistivity measurements of GPC to its actual chloride permeability level.

Read the full paper here: https://bit.ly/2KdyMoP