Waste Plasterboard Research Articles

Wastepaper fiber‐reinforced concrete containing metakaolin: Effect on fracture behavior

AbstractPlasterboard, a commonly utilized construction material, comprises a gypsum core nestled between two paper layers. Gypsum after demolition of plasterboards is a recyclable waste that has been reused into new plasterboard or other purposes such as agricultural products. However, there is a lack of understanding on the potential for recycling the paper layers. This study investigates the use of wastepaper fibers, obtained from the paper layers, as a reinforcing material and metakaolin as a partial cement replacement material in concrete. This study demonstrates the ability of the paper from waste plasterboard for reinforcing concrete. Wastepaper fibers were used at different concentrations ranging from 0 to 2.5% by weight of binder. Bending test was conducted for assessing fracture behavior of concretes, including load bearing capacity, modulus of rupture, crack mouth opening displacement (CMOD) at the load bearing capacity, fracture toughness, and fracture energy. Slump, axial compression, and scanning electron microscopy (SEM) were also conducted on the concretes. It is found that incorporating wastepaper fiber by up to an optimum content of 1.5% results in an increase in the compressive strength (57%), flexural load bearing capacity and modulus of rupture (31%), CMOD displacement at load capacity (14%), fracture toughness (37%), and fracture energy (73%) of the metakaolin‐based concrete. However, further increase in the wastepaper fiber content results in decreased mechanical properties of the concrete, which is due to the fiber agglomeration and non‐uniform distribution within the concrete matrix. Based on the results, the concrete with 20% metakaolin and 1.5% wastepaper fiber experiences similar mechanical properties to the conventional concrete. The results of this study underscore the substantial potential of leveraging waste materials such as wastepaper and by‐products like metakaolin to diminish reliance on conventional cement. This approach not only enhances the mechanical properties of concrete but also fosters sustainable building practices by promoting the recycling of waste materials, reducing carbon footprint, and mitigating the environmental impacts inherent in traditional concrete production.

Upcycling of waste plasterboard for the synthesis of high-quality gypsum-based 3D printing powder

A large number of waste gypsum was reused of low-value or landfilled which caused serious waste of resources. In this study, a high value-added recycling scheme for waste building gypsum to synthesize a 3D printable material with high-precision was designed. The α-hemihydrate gypsum (α-HH) was synthesized from waste plasterboard by the salt solution hydrothermal method. A synergistic optimization strategy was proposed involving the effect of sodium succinate and pH on the morphology and mechanical strength of α-HH. The properties of recycled α-HH were modified to meet the requirements of 3D printing, including fluidity, setting time and green strength. When the modifier dosage is 0.05 wt% and the pH is 5, the best morphology of α-HH crystals with an average aspect ratio of 1.07 (length of 10 μm) are synthesized. The converted product has close interlocking and intergrowth after hydration, which exhibits excellent mechanical strength (25.5 MPa). The 3D printing materials prepared by the composite modification of recycled α gypsum powder has proven to achieve good printable. The print errors smaller than 4% for pore objects larger than 4.0 mm, and satisfactory results are shown in terms of the strength and resolution of printing high detail cavity structures. This work provides a high value-added upcycling scheme for waste building gypsum that has great potentiality for future industrial application.

Enhancement of methane production and phosphorus recovery with a novel pre-treatment of excess sludge using waste plaster board

A new pre-treatment process for excess sludge is proposed to increase methane production and recover phosphorus by adding waste plaster board as calcium sulfate. The content of calcium sulfate in the plaster granules (PG) used in this study is 99%. When PG and calcium sulfate are added to the excess sludge generated from a municipal wastewater treatment plant, acetate production is enhanced as per sulfate reduction and phosphorus release is reduced via the formation of calcium phosphate. In the continuous pre-treatment experiment performed at 25 °C and for 10 days of sludge retention time (SRT) using calcium sulfate, 1935 ± 395 mg/L of acetate is produced with 1070 ± 255 mg/L of sulfate, which is reduced. Desulfobulbus spp., which can oxidize organic matter to acetate incompletely, have been observed in the pre-treated sludge. The pre-treated sludge has subsequently been used for methophiric anaerobic digestion. The methane yield from the pre-treated sludge is found to be 1.2 times that of the non-pretreated sludge at an SRT of 30 days, indicating that the pre-treatment using PG can improve methane production. Phosphorus is released from the non-pretreated sludge in the digester. Nevertheless, a decrease in phosphorus content has been observed, resulting in the digested sludge containing calcium phosphate that is useful for agriculture.

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.

廃石膏の硫化水素発生条件に共存する酸化亜鉛，酸化カドミウム，酸化水銀の挙動に関する研究

廃石膏の硫化水素発生条件に共存する酸化亜鉛，酸化カドミウム，酸化水銀の挙動に関する研究

Improvement Properties of Cohesion-Less Soil Using Recycled Bassanite

Solid waste management is a serious problem over the world. Therefore, reduction, re-use and recycling of waste have become major issues in recent days. Gypsum waste plasterboard is considered one example of these waste materials. This study evaluates the use of recycled bassanite, which is derived from gypsum waste plasterboard, to enhance the performance of two types of cohesion-less soil. Recycled bassanite was utilized as a stabilizing agent to improve both compressive and splitting strengths of the tested soil. The effect of bassanite content, soil type, water content and curing time were investigated to explore the behavior of treated soil with recycled bassanite. Test results showed that increase of bassanite content is associated with increase in optimal moisture content, while no significant increase in the dry unit weight was observed. Both compressive and splitting tensile strengths enhanced with the additives of recycled bassanite. The increase of bassanite content had a more significant effect on the compressive strength compared with the effect on tensile strength. The use of recycled bassanite to enhance the strength of sandy soil had a more significant effect compared with silty soil. The effect of curing time on the strength of treated samples was more significant in early curing ages compared with late curing ages. The strength decreased significantly in case of stabilized samples prepared with water content at the wet-side of the compaction curve. However, insignificant decrease in the strength of the stabilized sample was detected with moisture content at the dry-side of compaction curve. This research meets the challenges of our society to reduce the quantities of gypsum wastes, producing useful material from waste materials that will help to a sustainable society.

Study on Hydrogen Sulfide Gas Production Potential Test for Ground Improvement by Recycled Gypsum and Lime

Necessity to promote a recycle of waste plaster board is mounting, since the waste plaster board has been legally prohibited to dispose into inert landfill site. However, it is concerned that the recycled waste plaster board (recycled gypsum) produces hydrogen sulfide gas, so that it is one of the interference with the recycling. There is a possibility to control the hydrogen sulfide gas production from the recycled gypsum by artificially changing into alkaline condition or adding iron oxide. In this study, we discussed the hydrogen sulfide gas production from a ground improvement with the recycled gypsum, quick lime, and/or iron oxide powder. In addition, unconfined compression strength of the ground improvement is evaluated in order to obtain an incentive of the recycling. Adding only the recycled gypsum cannot improve strength of a soft ground having much amount of fine particles. Quick lime was required for strength improvement. If pH of the ground improvement is greater than 9, it was observed that the hydrogen sulfide gas production potential is negligible. Increasing pH by adding the quick lime is able to more effectively control the production of the hydrogen sulfide gas than adding the iron oxide powder. The production of the hydrogen sulfide gas is able to be controlled by adding the quick lime more than half of the amount of gypsum addition.

廃石膏ボードから再生した半水石膏の流動化処理土への適用に関する基礎的研究

廃石膏ボードから再生した半水石膏の流動化処理土への適用に関する基礎的研究

Fluoride Leaching Control of Waste Plasterboard Powder Using Light Burned Magnesite and Its Applicability to the Stabilization/Solidification of Clay

The reuse of waste plasterboard must be promoted more to maintain the residual capacity of the controlled type landfill sites because it is predicted that the amount of plasterboard retrieved with demolition works of building continues increasing for the time being. However, mixing the board comminuted while separating base paper namely the powdery dihydrate gypsum into ground, the leaching concentration of fluoride which has been contained in plasterboard since inception by coming from raw materials might exceed the environmental quality standards for soil pollution.The light burned magnesite has been early used for not only the improvement of soft ground but also the insoluble treatment of heavy metal pollution soil. Referring to such on-site achievements, we have made the samples which consist of powdery dihydrate gypsum, light burned magnesite and distilled water. Having added magnesite of 10% and water of 50% for the mass of gypsum, fluoride leaching concentration satisfied a target level (hereafter referred to as “insolubilization treated powder”). Moreover, regarding clay and sand mixed the insolubilization treated powder of which content was up to 30%, it was guessed that those might not re-leach fluoride under the stirring with an acid or alkaline water solution. Successively we performed the CBR test, box shear test and unconfined compression test to clarify a stabilization effect brought by mixing the insolubilization treated powder into clay. According to the results obtained from these tests, clay stabilized with the insolubilization treated powder surely indicated a tendency to increase bearing capacity and to develop strength as compared with clay in which only lime or cement was added.Judging from the novel findings mentioned above, it is possible to utilize the insolubilization treated powder as part of the soil materials.

Laboratory and Field Evaluations of Recycled Gypsum as a Stabilizer Agent in Embankment Construction

Approximately 1.6 million tons of gypsum waste plasterboard are produced annually in Japan. As such, it is essential to find an alternative way to reduce the quantities of this waste material to avoid environmental problems and the high cost of disposal in landfill. This paper describes a case study focused on the use of recycled gypsum, which is derived from gypsum waste plasterboard, to improve the strength of soft clay soil for embankment construction projects taken in consideration environmental impacts. Four different recycled gypsum contents ranging from 0 to 10% was investigated. Two different types of cements—Portland and Furnace slag type B—with a content ranging from 0 to 3% was used to develop solidification for recycled gypsum and improve environmental properties. For this purpose, a series of unconfined compression tests were conducted to evaluate strength performance of treated clay. While a series of environmental tests were conducted to explore the solubility concentration of fluorine, boron, and hexavalent chromium in the untreated and treated soil specimens. Furthermore, hydrogen sulfide and pH were investigated. Results showed that compressive strength and unit weight of treated clay soil increased with the increase of recycled gypsum content. The strength obtained in the field for treated soil with recycled gypsum was found to be greater than that obtained in the laboratory. The early curing days for soil-gypsum mixture had a significant effect on strength performance compared to the later days. The additives of recycled gypsum for tested soil swiftly increased the strength. This is a vital property for improvement embankment trafficability that helps to reduce the construction time and cost. The use of recycled gypsum within the investigated limits had no adverse effect on pH value and hydrogen sulfide gas was found to be less than the standard permitted limits. As well, the solubility concentrations for fluorine, boron, and hexavalent chromium were found within the permitted standard limits in Japan. The curing time had a significant effect on the reduction the release of harmful substance elements investigated. Furnace cement type B had the potential to improve the mechanical and environmental functions for soil-gypsum mixture. It is recommended that Furnace cement type B be used as a solidification agent for soil treated with recycled gypsum because it has low cost and it is more environmentally friendly than Portland cement.

Use of waste gypsum for trench backfill

In the UK, legislation is limiting the disposal of gypsum therefore alternative applications are encouraged. Large quantities of red gypsum arise from the production of titanium dioxide and from waste plasterboard. Both red gypsum and plasterboard gypsum were investigated for use in trench backfill. Red gypsum comprised filter cake lumps with moisture content of about 40% and up to about 100mm in size and plasterboard gypsum consisted dust to thin slab like particles with moisture content of about 20%. The latter was both with paper and without paper. The investigation undertaken aimed to develop gypsum-based trench backfill that required zero compaction, and could be mixed and placed using existing plant without specialist labor. Successful mixes containing waste gypsum, limestone quarry fines and Portland cement that complied with the existing specifications were developed. Tests included determination of unconfined compressive strength, soaked strength, resistance to freeze and thaw and sulfate contents. The sulfate levels in these mixes were within acceptable limits. The most suitable mix was evaluated in a short section of full-scale trial trench and was subjected to 1 million cycles of standard axle load. Deformation was found to occur only in the base course and wearing course layers.

Environmental effects on durability of soil stabilized with recycled gypsum

Abstract The use of recycled gypsum, which is derived from gypsum waste plasterboard, for ground improvement has recently been initiated in Japan and is not widespread around the world. As such, it is essential to explore the effect of environmental conditions on the performance and durability of soil stabilized with recycled gypsum. This is especially important in cold and rainfall regions such as in Japan, due to the solubility of gypsum. This paper presents an integrated experimental study to investigate the effect of environmental factors, in terms of freeze–thaw and wet–dry cycles, on the durability of soil stabilized with recycled gypsum. For this purpose, four different contents of recycled gypsum ranging from 0 to 20% were used. Four different cement contents ranging from 0 to 5% were used as solidification agent to optimize the cement content which is adequate to prevent the solubility and improve the durability. To study the effect of environmental factors on the durability, cylindrical specimens of stabilized soil were compacted at maximum dry unit weight and cured for 7 days under constant temperature and humidity. Subsequently, specimens were subjected to different numbers of freeze–thaw and wet–dry cycles. They were then tested for compressive strength, loss soil weight, and volume change. Results showed that compressive strength of stabilized specimens decreased while accumulated soil losses weight increased with the increase of both numbers of freeze–thaw and wet–dry cycles. Freeze–thaw cycles have a significant effect on the durability reduction of stabilized soil compared with the effect of wet–dry cycles. The durability of stabilized soil improved with the increase of both contents of recycled gypsum and cement. The 2.5% cement content is adequate to improve the durability of soil stabilized with recycled gypsum based on ground mechanical and economic functions. Both freeze–thaw and wet–dry cycles have insignificant effect on the volume change of soil stabilized with recycled gypsum. After using 2.5% of cement content, the strength of stabilized soil specimens increased slightly with the increase of wet–dry cycles; subsequent to that, the strength declined with increasing wet–dry cycles. Soil stabilized with only recycled gypsum and without any solidification agents, such as cement, is not durable against environmental conditions.

Investigation of recycled gypsum in conjunction with waste plastic trays for ground improvement

During the three stages of production, construction and demolition, approximately 15 million tons of gypsum waste plasterboard is generated annually in the world. It is considered a serious problem due to scarcity of land-filling space, increasing the cost of disposal and increasing environmental regulations. Investigations of using recycled gypsum “bassanite” which is derived from gypsum waste plasterboard and waste plastic trays for ground improvement were studied. Recycled gypsum was used as a stabilizing agent to improve the compressive strength while the waste plastic trays were used to improve the tensile strength. Recycled gypsum content, curing time and frost heave property throughout capillary rise test were investigated to determine the behavior of treated soil with recycled gypsum. In addition, size, content and aspect ratio of strips of waste plastic trays were investigated. Test results showed that increasing recycled gypsum content has a more significant effect on compressive strength compared to the tensile strength. The effect of curing time on the strength of treated soil samples with recycled gypsum is much pronounced in the early curing days compared to later ages. Adding strips of waste plastic trays to samples treated with recycled gypsum enhanced both splitting tensile and compressive strengths as well increased the value of secant modulus. Capillary rise rate was reduced with the increase of recycled gypsum content, which helps to reduce the formation of ice lenses; hence the susceptibility of treated soil against frost heave is increased. The size and content of strips of waste plastic trays have significant effect on the potential of capillary rise and the enhancement of strength and stiffness of tested soil.

Solidification Properties of Dredged Materials Stabilized with Waste Plasterboard Powder and Reinforcement Effect Brought by Wrapping the Mixtures in Geotextile

Though the sediments dredged from floors of lakes and ports are beneficial earth materials, the utilization is still stagnant due to continuing restraint of construction investment. On the one hand, plasterboard wastes occurring abundantly with the renovation and demolition works of building are recently bringing the stringency of a residual capacity at controlled type landfill site. In the present study, we have investigated the California bearing ratio (hereinafter referred to as “CBR”), unconfined compressive strength, resilient modulus and constant pressure shear strength after having stabilized the base material which was composed of lake mud, sea sand and waste plasterboard powder with equivalent quantities in dry mass. According to the results obtained from CBR-test and unconfined compression test, the mixing of a waste plasterboard powder reduced apparent water content in base material, and as an effect by this, the hardening progress with the passage of time certainly exceeded a difference of the stabilizer amount added. Successively, having examined the resilient moduli concerning mixtures with a material age of 28days, it was found that these values were equal to or greater than the existing granular base course materials. Secondly, we have examined relation between shearing stress and displacement for specimens (a diameter of 100mm and a height of 50mm) which were made by wrapping the stabilized base material in geotextile and have compared the strength parameter to specimens without covering. As a consequence, it was ascertained that the angle of shear resistance in specimens with geotextile became 10 to 25degrees larger than that in specimens without covering and that meanwhile the cohesion generally tended to become largish in the latter.

Effect of curing periods on unconfined compressive characteristics of cement-stabilized soils utilizing bassanite – beneficial use of waste plasterboard –

Effect of curing periods on unconfined compressive characteristics of cement-stabilized soils utilizing bassanite – beneficial use of waste plasterboard –

ポリエチレンによる石膏の高温還元の反応過程

Most of waste plaster board, which contains gypsum has been buried in the landfill. However, this treatment of waste gypsum board is becoming a serious problem due to lack of landfill capacity, and secondary pollution by toxic substance. In this study, we focused a recycle of calcium resources as CaO or CaS from the waste gypsum, and developed a reduction process of the gypsum using plastics at high temperature. Reduction behavior of CaSO4 by Polyethylene at temperature from 1273 to 1573K was studied with gravimetry and X-ray diffraction analysis. From the experimental results, we found that increasing CaSO4-CH2 gas interface tend to advance the reduction of CaSO4. Furthermore, direct formation of CaS from CaSO4 was observed only at temperature of 1273K without an intermediate compounds stage, and the reduction sequence was CaSO4→CaO→CaS at temperatures higher than 1373K. Finally, the sequence of reduction process for CaSO4 was discussed on the potential diagram of the Ca-S2-O2 system.

Development of bassanite production system and its geotechnical engineering significance - Recycling of waste plasterboard -

安価で耐火性，断熱性等に優れる石膏ボードは，建築資材として広く普及しているが，その生産量を反映して，建築物や住宅の解体によって発生する廃石膏ボードの量は近年益々増加している。このような現状から，処分場の容量不足に関する問題が指摘され始めており，廃石膏ボードのリサイクル技術の開発が急務であるといわれている。そこで本研究では，まず廃石膏ボードを再生するために，予め廃石膏ボードを紙と石膏とに分別粉砕した二水石膏に対して加熱処理を施し，水硬性の半水石膏に転化させる半水石膏生産システムを開発したので，その概要を報告する。さらに本システムから得られた半水石膏の地盤改良材としての有効性を明らかにするため，その半水石膏のセメント安定処理土への適用性を検討した。その結果，半水石膏の混入率と一軸圧縮強さ，乾燥密度および含水比との間に高い相関関係があることを明らかにし，廃石膏ボードから再生した半水石膏の地盤改良材としての有効性を実証している。

Recovery of Gypsum from Waste Plaster Board by Recrystallization Process

We propose a recrystallization process for recovering granular crystalline gypsum from waste plaster board, and the operating factors were investigated. The waste plaster board was mainly made from Gypsum (90% or more), insoluble organic materials like paper (1-5%), and inorganic materials like quartz (1∼4%). In the first stage of the process, the board was crushed in 2cm or less size and dehydrated in 75% or more dehydration rate. In the second stage of hydrating the dehydrated board, the needle-like gypsum in 15μm or less size were preferentially disintegrated from the board and recovered as under product in successive 325 mesh wet screening. In this case, the recovery of gypsum was affected by dehydration rate, solid concentration of hydration, agitation speed and hydration temperature. The experimental results showed that the optimum conditions for increasing gypsum recovery are as follows: dehydration rate of 75%, solid concentration at hydration of 20%, agitation speed of 250rpm, and room temperature. Under this condition, needle-like fine gypsum of 98.3% grade was recovered with 98.8% yield. This recovered fine gypsum was purified in the 3rd stage which is composed of dehydration in hot water of 97∼99°C. It was then, made to undergo re-crystallization at 60°C for 5hours and 325mesh wet screening. In this stage, plate-like crystalline gypsum of 159μm medium size was obtained with 99.1% grade and 92.8% yield.

Unconfined compressive strength of cement-stabilized soils containing bassanite produced from waste plasterboard

近年，産業廃棄物の大量化に伴う処分場不足が懸念されており，産業廃棄物のリサイクルが循環型社会形成のためにも重要となってきている。廃石膏ボードは，建築物や住宅の解体によって発生する廃棄物であるが，もしこの廃石膏ボードを建設材料として有効利用できれば，廃石膏ボードの処理問題や建設産業における天然資源の枯渇問題を解決できると考えられる。本研究では，廃石膏ボードのリサイクル推進のために，廃石膏ボードから再生した半水石膏を混入したセメント安定処理土の一軸圧縮特性について取りまとめている。半水石膏は，廃石膏ボードから得られる二水石膏を130°C以上で加熱することによって得られ，水と反応して短時間で硬化するという性質を有しており，その地盤改良材としての有効利用に期待されている。また，半水石膏は中性無害であるため，これまで使用されてきた強アルカリ性の石灰やセメント等に比べ環境に調和的である。実験結果から，半水石膏の添加率と一軸圧縮強さ，乾燥密度および含水比との相関関係が明らかとなり，廃石膏ボードから再生した半水石膏の地盤改良材としての有効性が示唆された。

Fundamental Study on Environment-Conscious Building Materials with Pulverized Waste Plaster Board

Fundamental Study on Environment-Conscious Building Materials with Pulverized Waste Plaster Board