Carbonation Depth Research Articles

Roles of particle packing and water coating thickness in carbonation and strength of γ-dicalcium silicate-based low carbon materials

In this work, a low carbon material of γ-dicalcium silicate (γ-C2S) was examined, with an emphasis on the properties influenced by its particle packing and water coating thickness (WCT). Differences in morphology and reactivity from that of cement particles render γ-C2S particles have different particle packing behavior and water film surrounding each particle. However, limited research has been conducted on it to deepen the understanding of γ-C2S-based materials. To fill this gap, the wet packing density of γ-C2S particles was measured and the WCT was varied at different water to solid ratios. At each WCT, the carbonated γ-C2S samples were characterized by techniques of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) consistently. Experimental results revealed little early strength gain when the WCT exceeded a certain value. Moreover, a critical carbonation depth was identified. Below the critical depth, the amounts and characteristics of carbonation products dominated, whilst above the critical depth, the strength gain was influenced by CO2 diffusion rate. An optimal WCT exists for achieving the highest strength and CO2 uptake. This work shall advance the development of low carbon γ-C2S-based materials from the perspective of particle packing.

Tree Based Approaches for Predicting Concrete Carbonation Coefficient

Carbonation is one of the critical durability issues in reinforced concrete structures in terms of their structural integrity and safety and may cause the fatal deterioration and corrosion of steel reinforcement if ignored. Many researchers have performed a considerable number of studies to predict the carbonation of concrete structures. However, it is still challenging to predict the carbonation depth or carbonation coefficient, as they depend on various factors. Therefore, creating a model that can learn from available data using Data Driven Techniques (DDT) is a step forward in this research field. This study provides new approaches to predict the carbonation coefficient of concrete through Model Tree (MT), Random Forest (RF) and Multi-Gene Genetic Programming (MGGP) approaches. With 827 case studies, the predicted models can be seen as a function of a set of conditioning factors, which are statistically significant in explaining the carbonation mechanism. The results obtained through MT, RF and MGGP were compared with those obtained through Multiple Linear Regression (MLR), Artificial Neural Networks (ANNs) and Genetic Programming (which were previously developed). The results reveal that the MT, RF and MGGP perform better than the previous models. Moreover, the MT technique displays its output in terms of series of equations, RF as multiple trees and MGGP in form of a single equation, which are more user-friendly and applicable in practice.

Report of RILEM TC 281-CCC: outcomes of a round robin on the resistance to accelerated carbonation of Portland, Portland-fly ash and blast-furnace blended cements.

Many (inter)national standards exist to evaluate the resistance of mortar and concrete to carbonation. When a carbonation coefficient is used for performance comparison of mixtures or service life prediction, the applied boundary conditions during curing, preconditioning and carbonation play a crucial role, specifically when using latent hydraulic or pozzolanic supplementary cementitious materials (SCMs). An extensive interlaboratory test (ILT) with twenty two participating laboratories was set up in the framework of RILEM TC 281-CCC ‘Carbonation of Concrete with SCMs’. The carbonation depths and coefficients determined by following several (inter)national standards for three cement types (CEM I, CEM II/B-V, CEM III/B) both on mortar and concrete scale were statistically compared. The outcomes of this study showed that the carbonation rate based on the carbonation depths after 91 days exposure, compared to 56 days or less exposure duration, best approximates the slope of the linear regression and those 91 days carbonation depths can therefore be considered as a good estimate of the potential resistance to carbonation. All standards evaluated in this study ranked the three cement types in the same order of carbonation resistance. Unfortunately, large variations within and between laboratories complicate to draw clear conclusions regarding the effect of sample pre-conditioning and carbonation exposure conditions on the carbonation performance of the specimens tested. Nevertheless, it was identified that fresh and hardened state properties alone cannot be used to infer carbonation resistance of the mortars or concretes tested. It was also found that sealed curing results in larger carbonation depths compared to water curing. However, when water curing was reduced from 28 to 3 or 7 days, higher carbonation depths compared to sealed curing were observed. This increase is more pronounced for CEM I compared to CEM III mixes. The variation between laboratories is larger than the potential effect of raising the CO2 concentration from 1 to 4%. Finally, concrete, for which the aggregate-to-cement factor was increased by 1.79 in comparison with mortar, had a carbonation coefficient 1.18 times the one of mortar.Supplementary InformationThe online version contains supplementary material available at 10.1617/s11527-022-01927-7.

Performance enhancement of rubberised-alkali-activated-concrete utilising ultra-fine slag and fly ash

This paper investigates the strength and durability properties of low calcium fly ash based rubberised alkali-activated concrete (RAAC) with a replacement of natural fine aggregate (NFA) with crumb rubber (CR) at different percentages. RAAC was prepared using a mix of Sodium silicate (Na2SiO3) and 8 M Sodium hydroxide (NaOH). The prepared specimens were cured at ambient room temperature and an elevated temperature of 60°C. The properties of RAAC, including density, slump, air content, compressive and flexural strengths, and elastic modulus were examined. The durability characteristics like carbonation depth, water penetration, and electrical resistivity were also investigated. The experiments indicated that slump, density, and strengths declined with increasing CR%. In addition, RAAC also displayed a higher water absorption and carbonation depth than conventional alkali-activated concrete (AAC) and was more prone to chemical, water, and chloride attacks. However, the higher electrical resistivity (ER) of RAAC indicated a higher compressive strength. The heat curing further enhanced the strength of RAAC and marginally improved its durability. Finally, the findings are supported with microstructural investigations. The heat-cured specimens possessed a comparatively denser microstructure compared to ambient-cured specimens. It is concluded that the discarded tyres can be used in RAAC production for structural applications, hence providing a sustainable solution for waste utilisation.

A STUDY ON CARBONATION DEPTH PREDICTION FOR CONCRETE MADE WITH GBFS CEMENT AND FA ADDITION

This paper presents the results of the examination of accelerated carbonation of concrete mixes made with CEM III / A blast furnace slag cement and the addition of fly ash. The test program was developed using an experiment design with two factors: a water-binder ratio and a fly-ash / cement ratio. Carbonation depth measurements were carried out according to FprCEN/TS 12390-12 (CO2 concentration = 4%, T = 20°C, RH = 55%). Associated tests were also carried out, including compressive strength, porosity, depth of absorption, water penetration depth, and capillary suction. Analysis of the test results allowed us to determine the influence of binder composition on concrete carbonization depth under standard test conditions. The results show that the carbonation depth increases along with the increase in the W/B ratio and as a result of the increase in the fly ash content in the binder. A mathematical model was developed to describe the carbonation process over time, which can predict the depth and rate of concrete carbonation. Furthermore, it was found that there is no close relationship between other properties tested (e.g. strength) and the depth of the carbonated concrete.

Inhomogeneities of carbonation depth distributions in recycled aggregate concretes: A visualisation and quantification study

The carbonation depths nonuniformly distribute in recycled aggregate concrete (RAC) because it has two kinds of mortars and three kinds of interfacial transition zones; but the inhomogeneity of the distribution is underestimated. Hereby, the inhomogeneities in RACs prepared with modelled industrially-produced and laboratory-produced recycled coarse aggregates (RCAs) were visualised and quantified using a proposed method. Afterwards, the influences of RCA types, RCA replacement ratios and strengthening methods of RCA on the average carbonation depths, their errors and the maximum carbonation depths were examined. The results showed that the carbonation depth distributions of RACs presented clear inhomogeneities. Utilising the CO2 curing technology for RCA might not reduce the inhomogeneities; but light effects can be observed through selecting a proper RCA or using a nano-SiO2 slurry soaking method for RCA. Reducing the maximum carbonation depth of RAC by selecting an appropriate RCA was more effective compared with by using the nano-SiO2 slurry soaking method. Besides, predicting the carbonation degree of RAC by using the maximum carbonation depth was more conservative than by using the average carbonation depth.

Effect of carbonation on chloride binding capacity of limestone calcined clay cement (LC3) and binary pastes

Carbonation of hydrated cement paste not only directly impairs the durability of reinforced concrete structures, but also alters the chloride binding capacity of cement-based materials. Besides, incorporating supplementary cementitious materials (SCMs) may influence both the durability against carbonation and the chloride binding capacity of binders. In this study, the chloride binding capacities of Limestone Calcined Clay Cement (LC3) pastes, prepared with four different kaolinite clays from local resources, have been investigated. In addition, binary pastes containing calcined clays (CC), silica fume and limestone powder (LS) as SCMs were designated to compare their pore structures, compressive strengths and durability properties with LC3 blends. The durability against carbonation was investigated via carbonation depth measurement, determination of hydroxide ions reduction and qualitative evaluation of phase assemblage changes through XRD analysis. Additionally, the chloride binding capacity of pastes was measured by the equilibrium method and the effect of carbonation on chloride binding capacity has been studied. The thermogravimetric analysis was also conducted to quantify the portlandite and Friedel's salt content of paste specimens. Based on the results, LC3 mixtures had lower bound chloride and Friedel's salt contents than binary blends prepared with CCs, while the chloride binding capacity of carbonated binary and ternary CC incorporated pastes were nearly similar. Besides, although LC3 pastes had higher chloride binding capacity than binary SF and LS containing blends, they were more susceptible to carbonation. Moreover, the CO3-AFm phases had generally lower capability to bind chloride ions than hydration products of LS-free binders.

Carbonation Depth and Chloride Ion Penetration Properties of Rubberised Concrete Incorporated Ground Blast Furnace Slag

Scrap tyres disposal revival the environmental concern except if recycled in an eco-friendly way. The inclusion of waste tyre crumb rubber (WTCRs) as a partial replacement of natural aggregate can be possible solutions for those concern. Thus, this study investigates the effect of using WTCRs at various contents (5, 10, 20 and 30% of volume) as a replacement agent of fine or/and coarse aggregate on water absorption, carbonation depth and chloride ion penetration rubberised concrete prepared with 20% ground blast furnace slag (GBFS) as Portland cement (OPC) replacement. Twelve batches are prepared by mixing the industrial wastes of GBFS and WTCRs. The results shown that modified rubberised containing 5% WRTCs as a substitute to natural aggregate, provided high durable performance such as lower water absorption, carbonation depth and chloride ion penetration compared to control specimen of traditional concrete. However, the rubberised concrete durability performance slightly trends to decrease with increasing WRTCs content from 5% to 30%, these proposed mix designs have a high potential for a wide variety of concrete industrial applications, especially in acid and sulphate risk.

Effects of citrate acid, solidum silicate and their compound on the properties of magnesium oxysulfate cement under carbonation condition

Additives including sodium silicate (SS) and citrate acid (CA) have been used to modify magnesium oxysulfate (MOS) cement. To improve the durability of modified magnesium oxysulfate (MMOS) cement and widen its application under carbonation environment, this paper reports experimental investigations into the mechanical properties, microstructural characteristics, and porous structure of MOS cement modified by CA, SS and their compound of CS by accelerated carbonization test. The properties were examined by mechanical strength tests, evaporable water test, X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetry (TG). Comparing to uncarbonated MOS and MMOS cements, 28 days of carbonation reduced the flexural strength by 20%-50%, and the compressive strength of cements modified by CA or CS was increased by 5%. Both CA and SS significantly improved the strength of carbonated or uncarbonated MOS cement, and CA required fewer time to achieve the mechanical strength similar to CS. Carbonation grated more MgCO3 and refined the porous structures of cement paste by reducing total pore and large pre. CA or CS at least reduced the brightness MOS cement paste by three times, whether they were carbonated or not. Microstructural analysis of samples collected in different carbonation depths further explained the modification mechanism from chemical composition perspectives. Finding of this study provide insights into the design of high-performance and sustainable MOS cement-based building materials under carbonation environment.

Experimental study and modelling of concrete carbonation under the coupling effect of freeze-thaw cycles and sustained loads

In cold areas, freeze-thaw (F-T) cycles and sustained loads are usually the two main factors affecting the carbonation resistance of concrete, which has been paid more and more attention. In this paper, the effects of F-T cycles and sustained loads on concrete carbonation were studied. An alternating experiment of carbonation and F-T cycles combined with stress was carried out and the carbonation degree was measured by the carbonation depth. Test results show that F-T cycles and sustained loads both have obvious influence on concrete carbonation. F-T cycles and tensile stress could weaken the carbonation resistance of concrete, and the coupling of them has a promotion effect on carbonation. However, since the influence of compressive stress on carbonation is opposite to that of F-T cycles, the coupling effect of the two factors on carbonation depends on which factor plays the leading role. Furthermore, a theoretical carbonation model was established according to the carbonation mechanism and modified to consider the coupling effect of F-T cycles and sustained loads on carbonation. The modified model was proved to have a high accuracy and can be used to predict the carbonation depth of concrete simultaneously subjected to F-T cycles and sustained loads.

Quantification of CO2 uptake of concretes with mineral additions after 10-year natural carbonation

The CO2 uptake of Portland cement, fly ash and blast furnace slag concrete cylinders was determined after 10-year natural carbonation. The purpose was to provide data to better assess the exchanges of CO2 during the life cycle of structures. The CO2 uptake of cylinders (mass of bound CO2 per unit of surface) was calculated from profiles of CO2 content determined by thermogravimetric and chemical analyses. The CO2 binding capacity of concrete with high slag content was found much lower than that of Portland cement concrete, due to the low degree of carbonation of CaO from slag. The CO2 uptakes of the studied specimens were however rather close. High carbonation depth of slag concretes compensates partly their lower binding capacity. The experimental results were compared to predictions of the European Standard EN 16757 model. The Standard model underestimates the CO2 uptake of concretes with mineral addition mainly because of an underestimation of the carbonation depth.

Reliability‐based recommendations for EN1992 carbonation cover design of concrete with coarse recycled concrete aggregates

AbstractResearch argues in favor of using recycled aggregates in structural concrete. However, lack of specific clauses in standards for recycled aggregate concrete design hinders the use of recycled aggregate concrete by the industry. Recycled aggregate concrete‐specific design clauses are hindered because conventional research must be complemented with experiments directed towards stochastic modeling, so that reliability concepts may evaluate whether the probabilities of failure of design comply with the expectations of Society or whether specific design rules are needed. This article compares the within‐batch variability of carbonation under accelerated conditions of four natural aggregate concrete and four analogue recycled aggregate concrete mixes and analyses the reliability of Eurocode 2 cover design for carbonation exposure. In general, the incorporation of coarse recycled concrete aggregates worsened the mean durability behavior of concrete, including resistance to carbonation. However, the variability of carbonation depth was not meaningfully affected by the recycled aggregates used (coarse recycled aggregates produced from concrete waste) and the reliability of concrete cover design only decreased due to the effect of the recycled aggregates on the mean resistance to carbonation. A 5 mm increase of concrete cover was found to more than offset the detrimental influence of full incorporation of recycled aggregates on the reliability of concrete cover design.

New insights into diffusion and reaction of CO2 gas in recycled aggregate concrete

The diffusion and reaction mechanisms of gas in natural aggregate concrete cannot be directly used for modelling the gas behavior in recycled aggregate concrete due to its inhomogeneity. Thus, the inhomogeneity of CO2 diffusivity in RAC is simulated for the first time using the multi-path modelling theory proposed herein. The diffusion and reaction models of CO2 in each path are then established. The carbonation depth in each path is determined. The reliability of theoretical maximum and average values of carbonation depths in different paths is further verified by experimental data. The results showed that there were five kinds of CO2 diffusion paths in recycled aggregate concrete and their carbonation depths showed a noteworthy difference. Besides, the developed theoretical model can predict the maximum value, weighted and mathematic average values of carbonation depths with reasonable accuracy, and the model in this study was more accurate than those in the literature.

Effect of Cementitious Materials on the Engineering Properties of Lightweight Aggregate Mortars Containing Recycled Water.

With the trend toward taller and larger structures, the demand for high-strength and lightweight cement concrete has increased in the construction industry. Equipment for transporting ready-mixed concrete is frequently used to bring concrete to construction sites, and washing this equipment generates a large amount of recycled water, which is an industrial by-product. In this study, we recycled this water as the pre-wetting water for lightweight aggregate and as mixing water, and we substituted blast furnace slag powder (BS) and fly ash (FA) as cementitious materials (Cm). In addition, we evaluated the fluidity, compressive strength, tensile strength, drying shrinkage, and accelerated carbonation depth of lightweight ternary cementitious mortars (TCMs) containing artificial lightweight aggregate and recycled water. The 28-day compressive strengths of the lightweight TCM specimens with BS and FA were ~47.2–51.7 MPa, except for the specimen with 20% each of BS and FA (40.2 MPa), which was higher than that of the control specimen with 100% OPC (45.9 MPa). Meanwhile, the 28-day tensile strengths of the lightweight TCM specimens containing BS and FA were ~2.81–3.20 MPa, which are ~13.7–29.5% higher than those of the control specimen. In this study, the TCM specimen with 5% each of BS and FA performed the best in terms of the combination of compressive strength, tensile strength, and carbonation resistance.

Influence of Fly Ash Dosage and Desert Sand Replacement Ratio (DSRR) on the Carbonation Resistance of Concrete

Carbonation of concrete causes corrosion of the steel reinforcement and reduces the service life of the structure. Based on the reality that fly ash discharge is increasing year by year and construction sand is becoming increasingly limited, it is of practical importance to study the effect of fly ash dosage and desert sand replacement rate on the carbonation resistance of concrete. Orthogonal test L9(34) with four factors and three levels was designed to study the influence of water-binder ratio, fly ash dosage, sand ratio and DSRR on carbonation resistance of desert sand concrete (DSC). The results of the orthogonal tests were analysed by range analysis and ANOVA and a comparatively better concrete mix ratio was given. Next, single-factor tests were designed to investigate the effects of fly ash and desert sand replacement rates on the carbonation resistance of DSC respectively. The regression model among carbonation depth, fly ash dosage and DSRR was established. The experimental results show that the carbonation depth of concrete with fly ash as a single variable increases with the amount of fly ash, increasing more rapidly in the early stages than in the later stages. As the DSRR increases, the carbonation depth of concrete with desert sand as a single variable first decreases and then increases and reaches its lowest value when DSRR equals 20%. When fly ash and desert sand are mixed into concrete simultaneously, the carbonation depth reaches minimum value on the condition that fly ash dosage is 10% and DSRR is 20%.

Research focused on low carbonation of concrete under old cement-based render

In-situ research and laboratory study of the concrete of old bridges shows that despite the low strength classes of concrete and the long time of exposure to CO2, it is possible to moderate the depth of their carbonation. Many old bridges were found during the in-situ survey in Slovakia, which showed negligible carbonation under an old cement render (PRC) even after more than 100 years of direct exposure to CO2. At the same time, it was found that if this protective layer was significantly damaged or missing in some places, the depth of carbonation of the same concrete reached considerable depths, locally 70-80 mm. The article presents and summarizes the findings from in-situ and laboratory research with a possible explanation of this phenomenon.

Effect of polyacrylamide on the carbonation behavior of cement paste

This work investigated the influence of polyacrylamide on carbonation behaviors of cement pastes by measuring carbonation depth and pH value. Electrochemical impedance spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and mercury intrusion porosimetry were performed to monitor changes in hydrates and microstructure of cement pastes to dissect underlying mechanisms. The results show that polyacrylamide decreases the amount of portlandite (CH) and alters its morphology from a larger size with parallel-stacked lamellar structure to a smaller size with edge-corroded structure, thereby enhancing CH reactivity with CO2 during carbonation. Higher Ca/Si ratios of C-S-H phases with a higher carbonation rate form in the presence of polyacrylamide. Polyacrylamide reduces porosity and improves pore refinement by transferring capillary pores to gel pores due to filling effect of CaCO3 grains with a small crystal size during carbonation. Overall, polyacrylamide yields an accelerating effect on the carbonation of cement paste in a dosage dependent manner.

Utilizing of coral/sea sand as aggregates in environment-friendly marine mortar: Physical properties, carbonation resistance and microstructure

The utilization of marine waste and resources to produce eco-friendly building materials is essential for the sustainable development of the construction industry on islands and coastal areas. The sea sand and coral sand sourced from coral waste are the most promising. Therefore, the objective of this work is to investigate the feasibility of coral/sea sand as fine aggregate to prepare an environment-friendly marine mortar. The effects of various volume fractions of coral sand intended to replace sea sand on the flowability, physical performances, carbonation resistance, and microstructure of the prepared marine mortars were evaluated. The experimental results showed that as the sea sand replacement by coral sand was increased, the flowability and dry bulk density decreased, while the water absorption increased. Encouragingly, usage of a combination of coral and sea sands enhanced the flexural strength of marine mortars. A mixture containing 80 vol% of coral sand showed the best effect. The carbonation depth of marine mortar was found to noticeably increase with increasing replacement ratios of sea sand by coral sand, closely relating to the increase in the volume of capillary and large pores. In particular, the combined utilization of coral sand and sea sand resulted in a compacted interfacial transition zone (ITZ) between fine aggregates and the matrix.

Microstructural examination of carbonated 3D-printed concrete.

The recent interest in 3D printing with concrete has generated great interest on how inhomogeneities arise and affect performance parameters, in particular strength and durability. With respect to durability, of particular interest is how 3D‐printed layer interfaces can impact transport of species of interest, such as moisture, chlorides or carbon dioxide in carbonation processes. This is of particular interest considering that the primary use case of 3D‐printed concrete has been as a lost formwork for a cast structural concrete, and thus it is of interest to determine the carbonation resistance. This study consists of a preliminary look at the microstructure after accelerated carbonation of a 3D‐printed concrete used as a lost formwork. Preferential carbonation is observed in the layer interfaces compared to the bulk of the printed filaments, possibly related to porosity from air voids or a locally high capillary porosity corresponding to the lubrication layer.

Effect of Equal Volume Replacement of Fine Aggregate with Fly Ash on Carbonation Resistance of Concrete.

Concrete is prepared by substituting an equal volume of fly ash for fine aggregate, and the effect of substitution rate on its carbonation resistance is studied. Using a rapid carbonation test, the distribution law of the internal pH value of concrete with fly ash as fine aggregate (CFA) along the carbonation depth under different substitution rates (10%, 20%, 30%, and 40%) after carbonation is studied and compared with the test results of phenolphthalein solution. Then, to further clarify the damage mechanism of fly ash replacing fine aggregate on concrete carbonation, the changes in the pore structure and micromorphology of CFA after carbonation are studied by means of mercury intrusion pressure and electron microscope scanning tests. The results indicate that the carbonation depth of CFA increases gradually with increasing carbonation time. In particular, in the later stage of carbonation, the carbonation rate of concrete decreases significantly with an increase in the substitution rate. The carbonation depth XC of CFA measured by phenolphthalein solution is approximately 0.24–0.39 times of the complete noncarbonation depth measured by the pH method. The pH value test is a reliable test method that can reveal the carbonation mechanism of CFA. Carbonation can significantly reduce the proportion of more harmful holes in concrete with a large amount of fly ash, but it can also increase the proportion of less harmful and harmful holes. In general, the pore size distribution and micromorphology of concrete can be improved by replacing fine aggregates with fly ash.