Microstructural Characterization of Prefabricated Hempcrete Blocks

Sustainable building materials have been developed to reduce the polluting emissions and the exploitation of natural resources of the building sector. Among these materials, an outstanding category is that of nature-based solutions which are produced recovering waste or by-products of agricultural cultivations and using them as vegetal aggregates to replace the traditional ones. This paper focusses on hempcrete which is produced mixing the by-product of industrial hemp cultivation (i.e., shives) and lime to obtain a sustainable, breathable and insulating material. The strength of hempcrete develops through carbonation of the binder that, leading to the formation of calcium or magnesium carbonates and mineralization of shives, determines the microstructure and hence most of the characteristic properties of the material. The aim of this research is to investigate how carbonation influences the microstructure of hempcrete when different recipes are used for blocks production. This study consists in the characterization of the material through techniques such as XRD (X-ray Diffractometry), SEM (Scanning Electron Microscopy) and TG-DTG (thermogravimetric analyses). Moreover, the evolution of carbonation is studied analyzing samples at different maturation times. The investigation of the carbonation reaction degree is also crucial to evaluate the environmental performances of the material because it allows the quantification of the carbon dioxide uptake. Also, periodic characterization allows to assess the durability of hempcrete and to select the best formulation according to the designed application and the corresponding service conditions.

Testing and Validating Instruments for Feedstocks of Mineral Carbonation

Different feedstocks Dunite, Olivine and Lizardite are examined in this research using various measuring techniques such as TGA-MS, XRD and Quantitative XRD and EDS. Quantitative XRD results matched with TGA-MS results. Malvern Mastersizer, EDS and QXRD results also showed a good match regarding the individuality of results which are shown graphically. TGA-MS calibration curves example is provided. Matching the results of different measuring techniques is a key to fundamental research. Comparison of the reactivity of dunite, soaked dunite, heat-activated dunite and lizardite and raw dunite soaked has been performed. TGA-MS and QXRD results match each other. Malvern Mastersizer, EDS and QXRD results match with their individual results indicating the instrument’s reliability. Semi-Quantitative XRD results authenticity is EXCELLENT. TGA-MS results match with QXRD is excellent. Mineral carbonation converts CO2 into stable mineral carbonates. This research explores the utilisation of serpentinised dunite (which is comprised of 61% lizardite) as a potential feedstock for mineral carbonation. Heat activation, ex-situ regrinding and concurrent grinding techniques were employed to enhance the reaction rate and yield, and to provide information on the carbonation reaction mechanism. Silica-rich layers that appeared during reference experiments were disrupted using concurrent grinding and significantly higher magnesite yields and Mg extractions were obtained.

Slurry-Phase Carbonation Reaction Characteristics of AOD Stainless Steel Slag

Argon oxygen decarburization stainless steel slag (AOD slag) has high mineral carbonation activity. AOD slag carbonation has both the resource utilization of metallurgical waste slag and the carbon reduction effect of CO2 storage. This paper aimed to study carbonation reaction characteristics of AOD slag. Under the slurry-phase accelerated carbonation route, the effect of stirring speed (r) and reaction temperature (T) on AOD slag’s carbonation was studied by controlling the reaction conditions. Mineral composition analysis and microscopic morphology analysis were used to explore the mineral phase evolution of AOD slag during the carbonation process. Based on the unreacted core model, the kinetic model of the carbonation reaction of AOD slag was analyzed. The results showed that the carbonation ratio of AOD slag reached its maximum value of 66.7% under the reaction conditions of a liquid to solid ratio (L/S) of 8:1, a CO2 partial pressure of 0.2 MPa, a stirring speed of 450 r.min−1, and a reaction temperature of 80 °C. The carbonation reaction of AOD slag was controlled by internal diffusion, and the calculated apparent activation energy was 22.28 kJ/mol.

Effect of Liquid Feeding Rate on Carbonation of Precipitated Calcium Carbonate via Continuous Method

Precipitated calcium carbonate (PCC) is an innovative product generated from lime that significantly offers various functional characteristics in fulfilling numerous market demand. PCC is produced by hydrating high-calcium quicklime resulting slurry so-called milk-of-lime and reacting the slurry with carbon dioxide (CO2) via carbonation process. The resulting PCC product is extremely white and typically has a uniform narrow particle size distribution. PCC is available in various crystal morphologies and sizes, which can be tailored to optimize performance in a specific application. The final properties of the PCC can be diversified by controlling processing parameters. In this current work, effect of liquid air pressure corresponding to feeding rate on a formation of PCC was investigated. In enhancing the product yield, the quicklime was initially converted into a solution containing calcium ion (Ca2+) using natural promoter agent. Subsequently, CO2 gas was continuously supplied into the Ca-rich ionic solution, thus inducing carbonation reaction to form PCC. This present work showed the carbonation time of producing PCC was effectively reduced as a function of feeding rate from 15 minutes at 10 psi to only 7 minutes at 50 psi. The PCC yield slightly increased from 19 g to 23 g with increasing the feeding rate from 10 psi to 50 psi, respectively. Morphologically, the PCC particles were dominated by rhombohedral structures at various feeding rates with an indication of intergrowth mechanism. This current finding signified the increasing feeding rate offered a significant reduction of PCC production time that might be efficiently applied by the industrial manufacturers.

Physicochemical characterization of the performance of acidified modified eggshell cyclic adsorption of CO2

The CO2 calcium based adsorbent was prepared by using citric acid monohydrate, L(+)-tartaric acid, glacial acetic acid and L(-)-malic acid modified eggshell. The cyclic calcination/carbonation reaction of the adsorbent before and after modification was carried out by thermogravimetric analyzer to investigate the attenuation characteristics of the cyclic CO2 absorption performance of the calcium-based adsorbent after modification. XRD, N2 adsorption analysis and other methods were used for physical and chemical characterization. The phase composition, morphology, specific surface area and porosity of the acidified calcium based adsorbent were investigated. The results showed that: during 20 cycles of calcination/carbonation after 900°C pre-calcination, the maximum carbonation conversion of CIES900 modified with citric acid is significantly higher than that of the previous adsorbent, and its maximum carbonation conversion is 90.7%. The L(-)-malic acid modified adsorbent MAES900 significantly enhanced the carbonation cycle stability of the adsorbent before modification, and the cycle stability reached 92.9%.

Effect of Graphene Nanoplatelet on the Carbonation Depth of Concrete under Changing Climate Conditions

Climate change has been unprecedented in the past decades or even thousands of years, which has had an adverse impact on the mechanical properties of concrete structures. Many researchers have begun to study new concrete materials. Graphene nanoplatelet (GNP) is an attractive nanomaterial that can change the crystal structure of concrete and improve durability. The aim of the present study was to investigate the effect of GNP (0.05%wt) on the carbonation depth of concrete under simulated changing climate conditions (varying temperature, relative humidity, and carbon dioxide (CO2) concentration), and compare it with ordinary concrete. When the concentration of CO2 is variable, the carbonation depth of graphene concrete is 10% to 20% lower than that of ordinary concrete. When the temperature is lower than 33 °C, the carbonation depth of graphene concrete is less than that of the control sample; however, above 33 °C, the thermal conductivity of GNP increases the carbonation reaction rate of concrete. When the humidity is a variable, the carbonation depth of graphene concrete is less than 15% to 30% of ordinary concrete, and when the humidity is higher than 78%, the difference in the carbonation depth between the ordinary concrete and the graphene concrete decreases gradually. The overall results indicated that GNP has a favorable effect on anti-carbonation performance under changing climate conditions.

Carbonation Resistance Classes of Concretes

Concrete carbonation is a phenomenon that occurs by the penetration into the cement stone of CO2 present in the atmosphere. The phenomenon occurs in the presence of water in which CO2 dissolves, forming carbonate ions, which in turn react with calcium ions in the pores of the concrete, resulting in calcium carbonate (calcite). The diffusion of CO2 occurs through pores and surface defects, it thus penetrates deeper into the concrete and the carbonation reaction can occur at a greater depth, eventually exceeding the thickness of the cover, causing corrosion of the reinforcement. [1] In the case of reinforced concrete bridges, corrosion induced by carbonation of concrete is one of the main causes of degradation. Thus, in the design stage of the reinforced concrete bridge structures, the inevitable process of carbonation of the concrete must be taken into account, in the design of the durability, by calculating the thickness of the concrete cover layer. This article aims to present the concept of carbonation resistance class, which will be a major change in the standard based on which the thickness of the concrete cover for reinforcement will be determined. This presentation is made in the context of the European performance approach to durability. In this sense, an analysis of the experimental results obtained in research on concrete prepared with different types of cements, carried out in collaboration with the laboratory of the Reinforced Concrete Structures Department, within the Technical University of Civil Engineering Bucharest. Proposals for classification in the carbonation resistance classes for concretes prepared with two types of cements are also presented.