Recycled Gypsum Research Articles

Improving Tailings Dam Safety via Soil Treatment

Mine tailings are the byproduct of mining activities, which need to be disposed of once the minerals in the ore are extracted. They can be disposed of in either dry or wet forms. The latter is most common, with the tailings being disposed of in the form of slurry inside retention structures. The retention structure may be a natural or manmade dam, with a predominant use of the upstream method due to its cost-effectiveness. This study analyzes the stability of an upstream tailings dam considering its staged construction. A two-dimensional nonlinear finite element model was developed using the program Plaxis 2-D to investigate the potential for stabilizing the tailings dam by using emulsified polymer and a mixture composed of cement kiln dust (CKD) and re-cycled gypsum (B). The numerical model demonstrated that utilizing a CKD: B mix increased the overall stability of the tailings impoundment above the conventional 1.5 safety factor requirements and indicated its usefulness in constructing robust dams whilst still being environmentally friendly.

Evaluation of gypsum waste for 3D decorative plate production

The concern with the amount of plasterboard waste produced during the process of construction and/or renovation, generates interest in studies that evaluate the reuse of this waste, avoiding the inappropriate disposal. In this way the present work has as its main objective to evaluate the use of gypsum waste in the production of 3D decorative plates. The gypsum was recycled through processes of cleaning, crushing, sieving and calcination at different temperatures. Cylindrical specimens and 3D decorative plates were developed with recycled gypsum without calcination and calcined recycled gypsum at temperatures of 150 ºC, 180 ºC and 200 ºC. These specimens were tested for compressive strength (cylindrical specimens) and flexural strength (3D decorative plates) 7 days after modeling. The results showed that there was no difference in compressive strength between recycled gypsum without calcination, recycled gypsum with calcination and natural gypsum. As for the flexural tensile strength, it was observed that the recycled gypsum without calcination had an average value 15% lower than the reference specimens.

Modification of Quaternary Clays Using Recycled Fines from Construction and Demolition Waste

Foundation of buildings in soft soil such as quaternary clay is often associated with difficult compaction, settlement, non-uniform and/or excessive deformation, and unsatisfactory shear resistance. The present study aims to assess the possibility of using recycled fines from construction and demolition waste, such as mechanically treated gypsum and waste concrete powder (WCP), instead of ordinary binders or industrial waste, in the stabilization of quaternary clay. A detailed characterization of soil components is presented. Seven mixes with various proportions of gypsum and WCP are prepared. Main geotechnical parameters of the modified soil are studied by applying standardized methods with a few deviations. XRD analysis and pH measurements are performed. It was found that the effect of 5% to 20% recycled di-hydrate gypsum is limited to improvement in moist soil compatibility. A gypsum content of 10% positively impacts soil cohesion and the oedometer modulus. WCP is an active component, containing non-hydrated cement, portlandite, calcite and calcium silicates hydrate. As a result, by adding 5% of WCP only, significant improvement can be achieved: greater soil cohesion, reduced deformability and higher UCS. When 5% of recycled gypsum is also added, soil cohesion is further improved because of ettringite formation.

Strength development and microstructure of recycled gypsum-soda residue-GGBS based geopolymer

The utilization of waste materials in road construction is one type of sustainable infrastructure practice, which reduces the dependence on natural resources. The waste, including recycled gypsum powder (from construction and demolition waste), soda residue (from the Na2CO3 industry), and ground granulated blast-furnace slag (GGBS), are favorable supplementary cementitious materials. This paper aims to evaluate the recycled potential of gypsum waste and wet-basis soda residue combined with GGBS to prepare geopolymer for subgrade applications. In this regard, the geopolymer mixture containing 0%, 5%, 10% recycled gypsum and 60%, 70%, 80% soda residue by dry weight will be prepared as partly substitute for GGBS. The mechanical performance will be measured using unconfined compression strength (UCS) and studied strength mechanism via scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Test results reveal that the strength of the RG-SR-GGBS based geopolymer decreased with increasing SR dosage and increased with increasing curing age. Excessive dosing of 10% recycled gypsum as a partial substitute for GGBS was detrimental to the strength of geopolymer, while a 5% dose was beneficial to increase the UCS value. The geopolymer of group SR60-RG5-S35 achieved a maximum UCS value of 9310 kPa at the curing age of 28 days. Ettringite (AFt) is a stable hydration product only if there is a sufficient supply of sulphate from recycled gypsum. Many rod-like AFt crystals form cavities in the geopolymer thus reducing the UCS value, while the right amount of AFt fills the capillary pores and increases the structural density and strength. GGBS was activated by the alkalinity of soda residue to generate dense calcium silicate hydrate (C-S-H gel), which is the main reason for the strength development.

Improved On-Site Characterization of Arsenic in Gypsum from Waste Plasterboards Using Smart Devices.

The impurities in waste plasterboards, a product of ethical demolition, are a serious problem for their recycling. Plasterboards, the wall materials used in old buildings, are often recycled into gypsum powder for various applications, including ground stabilization. However, this powder contains various chemical impurities from the original production process of the gypsum itself, and such impurities pose a risk of polluting the surrounding soil. Here, we present a simple method for verifying the presence of arsenic, a harmful element in recycled gypsum that is suitable for use at demolition sites. First, we developed a simple pretreatment method using a cation-exchange resin to dissolve insoluble gypsum suspended in water by exploiting a chemical equilibrium shift, and we estimated the quantity suitable for releasing the arsenic from arsenic-containing gypsum. This pretreated solution could then be tested with a conventional arsenic test kit by observing the color changes in the test paper using the image sensor of a smart device. This simple method could determine a wide range of arsenic quantities in the gypsum, which would be helpful for monitoring arsenic in recycled gypsum powder, thereby supporting the development of a safe circular economy for waste plasterboards.

Study on mechanical strength and water resistance of organosilicon waterproofing agent blended recycled gypsum plaster

In this study, organosilicon waterproofing agent blended recycled gypsum plasters (ROGPs) were prepared to determine their mechanical strength and water resistance. According to the results, the water to plaster ratio of ROGP increased steeply. Additionally, the mechanical strength and water resistance of ROGP decreased abruptly as the waterproofing agent increased, thus indicating the waterproofing agent’s loss of water resistance. Correspondingly, the water to plaster ratio and mechanical strength of organosilicon waterproofing agent blended commercial gypsum plasters (COGPs) slightly increased and decreased, respectively. Furthermore, the water resistance of COGP increased, and the suitable waterproofing agent was 1.0 %. The analysis shows that the large aspect ratio of ROGP and long-chain polymers increase their water to plaster ratios, whereas their mechanical strength and water resistance decrease owing to the resulting large plate-shaped crystals and poor overlapping between the crystals in hardened ROGP. The loss of water resistance is consequence of the oxidation of Si-H in ROGP. Therefore, different mechanical strength and water resistance development trends could be observed in ROGP and COGP. In principle, this study will contribute to the efficient utilization of recycled gypsum plaster.

Recyclability Process of Gypsum Reinforced with Hemp Fabrics: Impact and Flexural Behaviour

Gypsum is an ancient material, still widely used and suitable for many applications in the constructions due to its low cost, availability, lightweight, good thermal and sound isolating behaviour, fire resistance and low energy consumption. One of the most established application is its use as building walls and as pointed out in authors previous research works, it can be very useful and interesting to reinforce the gypsum with vegetable fibres like hemp. This aspect is in line with the current world situation where every industrial company needs to decrease the materials waste, increase recyclability and use more eco-friendly materials. Therefore, this work aims at designing, manufacturing, and testing of both commercial and recycled gypsum specimens reinforced with hemp fabrics, in order to improve impact and flexural resistance of traditional gypsum boards. The recycling process was carefully studied to detect the best grinding time, temperature and time of the heat treatment required to allow the reutilization of gypsum powders. Three point bending and impact tests at different energy levels were carried out in order to understand how the presence of the hemp fabrics within the gypsum matrix and how the recycling process affect the mechanical response of reinforced gypsum.

Life cycle assessment of natural and recycled gypsum production in the Spanish context

Spain occupies a very prominent position as a world producer of gypsum. Consequently, the industrial processes are more refined, as the production volumes of the factories are much higher than in other countries. Therefore, the environmental impacts of the production of one ton of gypsum are significantly lower. However, new cleaner alternatives must be studied to promote more sustainable construction. In that sense, this paper aims at studying the environmental assessment of the production of natural and recycled gypsum in the Spanish context. In order to conduct the environmental analysis, a from cradle to gate life cycle assessment (LCA) was carried out, using the Impact 2002 + methodology. All the input data was obtained from a medium-size gypsum manufacturer located in Jaen (Andalusia), one of the best regions in terms of gypsum purity. The results for all the scenarios under study were analyzed separately and compared with previous studies published by other investigators and manufacturers’ reports data. Contrary to most other previous researches, the LCA was performed on the basis of primary data given by the producer, and the regional factors were also taken into account.The results achieved in the LCA showed for the production of recycled gypsum (from plasterboard and powder waste) a significant improvement (more than 40%) in all the impact categories understudy, as compared to the natural gypsum production. Furthermore, the results obtained for the endpoint indicators showed an important reduction (56 and 58%) of the environmental impacts when recycled gypsum production was compared with the natural one. On the other hand, it was reaffirmed that the natural gypsum production process in Spain is less environmentally harmful than in other countries.

Response of Soft Soil Mixing with Recycled Gypsum (Plasterboard) as Stabilized Agent for Soil underneath oil tank as a case study

Soil stability plays a vital rule in projects’ infrastructure such as embankment, retaining walls dams and highway. Structure built on soft soil may experience uncontrollable settlement and critical bearing capacity. This may not meet the design requirements for the geotechnical engineers. Soil stabilization is a process to change such undesirable properties in order to meet the requirements. The main objective of this study is to evaluate the use of recycled gypsum, which is derived from gypsum waste plasterboard, as a stabilized agent for soft clay. Twenty eight experimental tests have been conducted to improve a soil brought from a site in Basra (Garma Ali/south of Iraq) using four different recycled gypsum percentage varying from 0 to 15%. The properties which have been studied are grain size distribution, Atterberg limits, unconfined compressive strength, and compressibility. The results indicate that as the gypsum contents increase, the liquid limit decreases up to gypsum content of 3% and then increases. The plastic limit has been decrease up to 7 % of the gypsum content and then increases. Furthermore, the maximum dry density decreases while the optimum moisture content is increased as the percentage of gypsum content has increased. The compression index (Cc) has increased as the gypsum content increases while the swelling index has increased up to 5% then it has decreased. The unconfined compressive strength has increased by adding recycled gypsum up to 5% while it is reduced as the percentages of gypsum has increased beyond 5%. Adding 5% of recycled gypsum raise the bearing capacity to approximately 167% compared with the bearing capacity of untreated one.

Comparison of physical and mechanical properties of civil construction plaster and recycled waste gypsum from São Paulo, Brazil

This paper describes the physical and mechanical properties of powdered, paste and hardened materials obtained by recycling plaster waste collected at civil works. Recycling of waste generated in all sectors of society has become increasingly important for environment protection. Since gypsum waste has the same chemical composition of the rock that gives rise to the hemihydrate form after calcination at moderate temperatures (~ 150 °C), recycling becomes attractive by simply calcining the residue to generate a new hemihydrate. The objective of the reported work is to compare recycled gypsum waste to commercial plaster, as well as comparing a mixture of waste with commercial plaster. Both apparent bulk density and bulk density decreased with increasing content of recycled plaster in the mixture, while the setting time, water content to normal consistency and compressive strength all increased. The recycled plaster alone could be considered satisfactory for this kind of application, with no need for blending it with the commercial one. Furthermore, TGA and XRPD quantitative phase analysis by using the Rietveld method indicated that the microstructure of the recycled material presented no differences from the original one, which demonstrates the viability of this recycling process.

Techno-economic impact assessment of recycled gypsum usage in plasterboard manufacturing

Recycled gypsum derived from post-consumer sources is a promising resource that can be reincorporated in the production chain, offering opportunities to decrease manufacturing costs given its significantly lower price compared to conventional gypsum. The systematic usage of post-consumer recycled gypsum is a relatively new practice in the plasterboard industry and there is lack of extensive literature references on the potential effects on the manufacturig process, since the available related studies are limited to more holistic approaches. The current work is, to our knowledge, the first study to assess the practice of gypsum recycling from an economical and technical point of view within the boundaries of the plasterboard manufacturing process. The paper provides a detailed techno-economic impact assessment of the usage of recycled gypsum up to 30% by weight in feedstock in the manufacturing of Type A plasterboard, based on data collected from full-scale industrial production trials carried out in five representative European plants located in four different countries. The potential impacts are analyzed in relation to each affected process parameter. A series of options for process adjustments, modifications and corrective measures in order to amortize the effects on product quality and/or cost are also reported. The analysis indicates high dependence of the cost impacts on process-specific characteristics. A limited reduction of 0.6% in the average total manufacturing cost per m2 of plasterboard was calculated, which can be associated to the considerable decrease, by 9.5%, of raw material costs. The latter fully compensates the increases to other process costs, and mainly to chemical additives which increased by 8%. The overall analysis allows quantification of the process parameters and costs that are affected when the percentage of recycled gypsum incorporated in plasterboard production is significantly increased. The results and the methodology proposed in the study can serve as a basis for a representative cost impact assessment of high-percentage recycled gypsum incorporation in any typical plasterboard production line plant. The methodology can serve as a guideline for techno-economic assessment of industrial production lines where the input datasets originate from different plants and can be characterized as “non-homogeneous” due to case-specific differences.

Multi-criteria decision analysis to assess the environmental and economic performance of using recycled gypsum cement and recycled aggregate to produce concrete: The case of Catalonia (Spain)

The production of virgin raw materials used in construction and the generation of construction and demolition waste (CDW) are key environmental issues in the construction industry. Portland cement and concrete are used extensively in the construction sector. Processing of CDW to produce recycled gypsum cement and recycled aggregates (RA) and their use in the production of structural and non-structural concrete are one way of slowing natural resource depletion and reducing the amount of CDW landfilled. This study proposes the application of multi-criteria decision analysis (MCDA) to compare the production of “green” concretes made from recycled gypsum cement (RGC) and RA with the production of conventional concrete made from natural aggregate and ordinary Portland cement. The VIKOR MCDA method was employed to determine the best or a set of good alternative(s) for concrete production, considering environmental and economic criteria. The life cycle assessment method was used to select the environmental evaluation criteria, and the reference cost of producing concrete alternatives in Spain was used to determine economic criteria. The results of this study, in which environmental and economic criteria were considered of equal weight, or one of the two criteria was given greater weight, showed that the best option for structural and non-structural concrete was the use of RGC and RA. In both cases, the worst alternative was conventional concrete. In conclusion, we found that the use of RGC and RA in concrete production is positive because it replaces the original raw material, reduces the environmental impact, and lowers the economic costs.

Characterization of quality recycled gypsum and plasterboard with maximized recycled content

The quality of secondary materials is imperative to promote a circular economy. In order to improve the way in which the quality of recycled gypsum is assessed, European guidelines on recycled gypsum (RG) quality criteria have been outlined in the framework of the Life+ Gypsum to Gypsum (GtoG) project. Such GtoG guidelines, along with the European Standard on gypsum plasterboard EN 520, provided the basis for this study. During the GtoG project, gypsum recycling and plasterboard manufacturing processes were monitored by testing the gypsum feedstock and the plasterboard produced. The aim of this paper is to discuss the results obtained on relevant parameters that characterize gypsum as a secondary raw material, as well as the resulting product. The minimum requirements were fulfilled by 56% of the RG samples and 86% of the plasterboard with increased RG.

Effect of different ways of STPP retarder addition on properties of recycled gypsum

We analyzed the influence of sodium polyphosphate (STPP) on the performances of recycled gypsum (RG). This analysis was performed with two different ways of STPP addition: One was that the STPP was added into Plaster of Paris (POP), then recycled plaster (R-SP) was obtained after a series of processes and the other was that the STPP was directly put into recycled plaster (R-PS). The conclusions confirmed that STPP increased the water demand and delayed the hydration of R-PS. With regard to its hardened performance, STPP provided hardened recycled gypsum with a loose structure which led to the lower strength and higher water absorption than recycled plaster (R-P) without STPP. On the contrary, the water requirement and the setting time were decreased and shortened by STPP in R-SP, respectively. A dense structure was also possessed by R-SP which contributed to the high strength and low water absorption. The analysis shows that STPP is selectively chemisorbed on the (111) face of R-PS crystals, it inhibits the growth in c axis direction, resulting in the extending of setting time and the transformation of morphology, making the hardened R-PS crystals coarsened, which results in high W/P and low strength. Whereas the low W/P is made by both the rod-like crystals of low length-radius possessed by R-SP and the relatively high ζ-potential absolute value caused by — (PO3Ca) on the surface of R-SP, leading to the complete development of crystals and their close overlapping, thus bringing about the increase of strength.

Best practices for the management of end-of-life gypsum in a circular economy

While gypsum can effectively be recycled, most gypsum waste (GW) is currently landfilled in the European Union. In order to achieve higher recovery rates and promote a closed-loop supply chain, it is necessary that stakeholders can implement best practices, in particular from waste production to waste processing, processes that are part of the end-of-life (EoL) stage. In this stage, waste production cannot be reduced, and therefore the priority should be to appropriately collect and recover EoL products. The aim of the paper is to investigate best practices for the management of EoL gypsum in a circular economy. To achieve this, best practices for the management of EoL construction products are selected from the literature, adapted to the case of EoL gypsum and subjected to stakeholder consultation. Results revealed significant differences in the waste management practices between two target groups: gypsum recycling and non-gypsum recycling countries. It is concluded that three best practices are fundamental to promote a circular economy for gypsum products: on-site segregation of GW, clear waste acceptance criteria and clear recycled gypsum quality criteria.

THE DIFFERENCE ON COMPRESSIVE STRENGTH AND DIMENSIONAL CHANGE OF COMMERCIALLY TYPE III GYPSUM COMPARED TO RECYCLE GYPSUM TYPE III TO PRODUCE WORKING CAST

Gypsum is derived from pure calcium sulfate dehydrate which is a common material that is commonly used in denture manufacturing process. This study aimed to know the difference on compressive strength and dimensional change of commercially type III gypsum compared to recycle type III gypsum to produce working cast. The type of research is laboratory experiment. A total of 40 samples for each test is divided into five groups which consists of commercial type III gypsum, pure recycled type III gypsum, pure recycled type III gypsum with 10%, 20%, 30% type III commercial gypsum. The difference on compressive strength and dimensional change between the groups was analyzed using one way ANOVA and is them tested with LSD test. The result showed that there was a significant difference (p<0,05) between compressive strength and dimensional change of commercial type III gypsum compared to pure recycled type III gypsum and pure recycled type III gypsum with 10%, 20% and 30% type III commercial gypsum. In conclusion, addition of 30% commercial gypsum in recycled gypsum the compressive strength was higher than other recycled gypsum types.

Energy Analysis of the Effects of High-Level Reincorporation of Post-consumer Recycled Gypsum in Plasterboard Manufacturing

The reincorporation of post-consumer recycled gypsum has recently started to be implemented in plasterboard manufacturing by the European gypsum industry. Plasterboard manufacturing in Europe, despite its energy intensiveness, has practically reached its maximum energy efficiency levels, with little or no room for further energy saving measures. However, the potential impacts of the reincorporation of post-consumer recycled gypsum in feedstock on a systematic basis and at high rates have not been evaluated within the strict scope of the process based on so far existing studies. In this respect, the present work aims to identify and quantify any such impacts on thermal and electrical energy flows, focusing on a closely defined scope that includes only the process steps potentially affected by recycled gypsum usage. The paper investigates the incorporation of recycled gypsum up to 30 % in Type A plasterboard manufacturing in terms of its effects on the energy consumption of the process, based on consolidated data recorded during full-scale industrial trials carried out in five large European plasterboard plants with typical production lines. The results show a marginal average overall increase in total energy consumption of 0.1 % as the net effect of small variations caused in the thermal and electrical energy consumption (0.2 % drop and 2.9 % increase respectively). The marginal overall result falls within a relatively broad estimated range of uncertainty of −9.1 to +10.4 % due to the anticipated variation of data emerging from full scale industrial trials, and cannot be considered conclusive. However, the analysis undoubtedly shows that recycled gypsum usage directly or indirectly affects the energy consumption of the process highly depending on process-specific characteristics and recycled material quality, leaving possible room for significant energy savings through optimization and accounting for process particularities, as evidenced by the range of impact results on individual plant level.

Grindability, grading and wettability of recycled plaster

The changes of grindability, grading and wettability of recycled plaster(R-P)and the mechanisms of these changes were studied by using vickers hardness, particle size distribution(PSD), scanning electron microscope (SEM) and nitrogen adsorption porosimetry to reveal that R-P was obviously different from plaster of Paris(POP). At the same milling time, R-P had the characteristics of high specific surface area, fine particle diameter and uneven size distribution compared with POP, so R-P possessed both good grindability and poor grading. The water absorption, dissolution rate and mass loss in dry-wet cycle of the hardened recycled gypsum(hardened RG) increased, while the water saturated strength and dry-wet cycle strength decreased significantly compared with the hardened virgin gypsum(hardened VG). Therefore, poor wettability could be seen in R-P. The analyses indicated that the changes of grindability and grading could be attributed to the reduction in hardness and the increase in the porosity of hardened RG and that the poor wettability of R-P was caused by the increase of large pores and the changes of microstructure of hardened RG.

Indicators to Measure the Management Performance of End-of-Life Gypsum: From Deconstruction to Production of Recycled Gypsum

The management of the end-of-life (EoL) stage of a product directly affect the destination of EoL products. In the construction sector, EoL processes such as building deconstruction or conventional demolition commonly determine whether the material flows cycle is closed. In this context, increased knowledge on the EoL processes is considered vital for enabling stakeholders to make better informed decisions on each process. Pertinent parameters and key performance indicators may assist in this task, through the acquisition of relevant data that measure progress against targets. This paper focuses on EoL gypsum, a non-inert material appropriate for closed-loop recycling. In particular, a set of performance indicators are developed with the aim to increase the amount of gypsum waste capable of being recycled. At the same time, the production of quality recycled gypsum (RG) is prioritized. To this end, monitoring parameters were first defined and combined in the form of monitoring indicators. Such indicators were subsequently used in five pilot projects (from building deconstruction to production of recycled gypsum) set in four national contexts: Belgium, France, Germany and the United Kingdom. After data collection and analysis, 17 best practice indicators are identified out of the initial indicators, which recognize and encourage best practices associated to the recycling route, from a technical, environmental, social and economic perspective. The ideal conditions to produce RG from EoL gypsum are then formulated.

Life cycle energy and material flow implications of gypsum plasterboard recycling in the European Union

Turning waste into a resource is a way to increase resource use efficiency and close the material loop of a circular economy. Gypsum plasterboard is well suited for this, because the raw material calcium sulphate dihydrate (CaSO4·2H2O) can repeatedly change its properties through a reversible hydration reaction. The waste hierarchy is applied when plasterboard is recycled instead of landfilled, which contributes to the European 2020 target of 70% recovery of construction and demolition (C&D) waste, as defined in the Directive 2008/98/EC on Waste. This paper evaluates the energy and climate impacts of different levels of plasterboard recycling. First, we formulate a life cycle model of gypsum mass flows in the European Union (EU-27) in the reference year 2013. This model constitutes the basis of the quantitative scenario analysis. Secondly, we assess the material flows, energy use and greenhouse gas (GHG) emissions in different recycling scenarios. We compare the current situation (“2013 base case”) to two scenarios: a worst case scenario of 0% recycled gypsum (“Zero recycling case”), and a best case scenario of zero gypsum waste sent to landfill, corresponding to 18.7% recycled gypsum in new plasterboard (“High recycling case”). We find no significant variation between scenarios in terms of life cycle energy use, as lower impacts from gypsum mining, transport of natural gypsum and final disposal in the best case scenario are balanced by the energy for the transport of plasterboard waste and recycled gypsum and for material pre-processing during manufacturing. In contrast, life cycle GHG emissions are lower as recycling increases, largely driven by the degradation of plasterboard lining paper in landfills.