Inclusion of spend garnets as sand replacement enhances compressive strength of AAMs.Spend garnets AAMs improve durability and reduce drying shrinkage problems.Development of sustainable and low-CO2 emission construction materials.
This paper investigates the possibility of using garnet waste as river sand replacement in high-strength alkali-activated mortars (AAMs) containing fly ash (FA) and ground blast furnace slag (GBFS). The garnet waste replacing river sand was used at varying levels of 0, 25, 50, 75, and 100%, by weight. In this study, the ratios of binder to aggregate (B:A), alkaline activator solution to binder (S:B) and the activator solution modulus (Ms) remained the same in all samples tested. The tests conducted were slump flow, compressive strength, flexural strength, drying-shrinkage, porosity, and resistance to acid, etc., which indicated the impacts of using garnet waste on the mechanical and durability performance characteristics of AAMs. The tests data revealed that as the level of waste garnet content increased in AAMs, there was a corresponding improvement in the workability of said samples. Notably, when the garnet waste content level exceeded 25% in the tested samples, there was a decrease in flexural and compressive strength in comparison with the control sample. Therefore, it would appear that the garnet waste could act as a potential replacement of river sand up to a maximum of 25% without any strength loss. It also meets the need for a cost-effective alternative which is eco-friendly and a renewable resource. It is recommended that spend garnets waste should be used in AAMs as river sand replacement to minimize the environmental problems, cost and natural resources depletion.
Rapid industrial growth has witnessed the ever-increasing utilization of sand from rivers for various construction purposes, which caused an over-exploitation of rivers beds and disturbed the eco-system. strong engineering properties of waste garnets offer a recycling alternative to create efficient construction materials. Recycling of garnets provides a cost-effective and environmentally responsible solution rather than dumping it as industrial waste. In this spirit, this article presents an investigation into the capacity of spent garnets as sand replacement. The main parameters studied were the evolution of leaching performance, microstructure of the raw spent garnet and sand specimens. The microstructures, boning vibrations and thermal properties of the raw materials were determined using X-ray diffraction (XRD), field emission scanning microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, and thermo gravimetric analysis (TGA). Admirable features of the results suggest that the spent garnet is proven to be suitable replacement of sand. It is established that proper exploitation of spent garnet as an alternative to sand could save the earth from depleting the natural resources which is essential for sustainable development.
In the construction sector, river sand has turned into a costly material due to various reasons. In the current study, used foundry sand (UFS) and spent garnet sand (SGS) are used as a partial and full replacement to sand in concrete production.
The objective of the work is to develop non-conventional concrete by replacing river sand with a combination of UFS (constant 20Wt.% replacement) and SGS at various percentages (20, 40, 60 and 80 Wt.%).
Compared to conventional concrete, the 28days compressive strength of non-conventional concrete (with UFS at 20% and spent garnet sand at 20%, 40% and 60% were 8.12%, 6.77% and 0.83% higher, respectively. The 28days split tensile strength of non-conventional concrete (UFS at 20% and SGS at 20 and 40%) were 32.2% and 51.6% higher, respectively.
The results showed that combined SGS and UFS can be used as a partial replacement of river sand in the manufacturing of concrete that is used in all the applications of construction sector such as buildings, bridges, dams, etc. and non-structural applications such as drainpipes, kerbs, etc.
The author wishes to gratefully acknowledge the UG students Mr Dileep Kumar and his team for the work support. The author also acknowledges the GMR Institute of Technology for providing the laboratory facilities in conducting this research work.
Kanta, N.R. and Ponnada, M.R. (2021), "Performance of spent garnet sand and used foundry sand as fine aggregate in concrete", World Journal of Engineering, Vol. ahead-of-print No. ahead-of-print. https://doi.org/10.1108/WJE-10-2020-0514
Garnets are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. This mineral group shows a range of hardness on the Mohs scale of about 6.5 to 7.5. Garnet sand is a good abrasive, and a common replacement for silica sand in sand blasting.
When we use garnet sand in surface blasting, since garnet sand has a high specific weight, it generates less dust during blasting process, which guarantees safety of operators and improves visibility. In comparison, quartz sand is a kind of abrasive that is easy to be broken. During blasting process, it will produce large amount of harmful gas and hydrated silica dust polluting the environment. Once taken in by human, these dust may cause cancer.
Garnet sand can be used in a variety of fields. Generally, it can be reused five times and more. When garnet sand loses its cutting capacity, it can be used as cement additive in construction industry.
Garnets being the waste spin-off of surface treatment operations remain a major environmental concern worldwide. Robust engineering properties of these waste garnets offer the opportunity to get efficient construction materials via their appropriate recycling. In this spirit, we evaluate the capacity of spent garnets as sand replacement for achieving self-compacting geopolymer concrete (SCGPC). Such SCGPC specimens are prepared using ground granulated blast furnace slag (GGBFS) wherein the river sand is replaced by spent garnet at varying contents (0100%) under constant Liquid/Binder (L/B) mass ratio of 0.4. Performance evaluations of the developed SCGPC samples are made using several tests including durability, workability, flexural, compressive, splitting tensile strength conforming the EFNARC standard. Test results revealed an enhancement in the workability of the proposed SCGPC specimen with the increase of spent garnet contents. Furthermore, other strengths are discerned to be lower compared to the control sample at all stages of replacement. It is established that the spent garnet is prospective candidate for sand replacement up to 25% in terms of environmental amiability, cost effectiveness and conservation of natural resources.
Lately, intensive researches have proven that modified concretes obtained via waste materials incorporation can lead to sustainable product development. Such concrete structures not only allow greener environmental growth in the construction sector but also protect the excessive consumption of natural fine aggregates that depletes the innate resources . Rapid industrial growth has witnessed the ever-increasing utilization of river sand for building purposes where river beds are worn-out. Several problems are emerged including the increase of river bed depth, lowering of the water table, increasing salinity and destruction of river embankments . Thus, exploration of alternative materials as a fine aggregate in concrete to replace the river sand became an absolute necessity. In this regard, garnets are emerged as a promising candidate to fulfil such requirements.
The generic word so called garnet refers to a group of complex silicate minerals having analogous lattice crystalline structures and varied chemical compositions . Interestingly, the angular fractures and hardness properties of garnets together with their ability to be recycled make them advantageous for numerous abrasive functions. Garnet has chemical composition of A3B2(SiO4)3 [A: Ca, Mg, Fe or Mn; B: Al, Cr, Fe or Ti]. Garnets have major industrial uses such as water jet cutting, abrasive blasting media, water filtration granules, abrasive powders, etc . A recent assessment on a Malaysian shipyard industry revealed that this country imported 2000 million tons of garnets in the year 2013 alone and a large quantity was dumped as wastes. Generally, abrasive blasting technique is used to prepare the surfaces for coating and painting . This technique is used for the construction of vessels, ship maintenance and repair activities. Thus, blasting process creates large quantities of exhausted garnet wastes mixed with surface elements such as paint chips and oil. Such garnet wastes cause many environmental and health hazards such as water contamination when these materials are entered in the waterways during flood or through runoffs. Therefore, spent garnets pose a threat to the ecological balance and biodiversity.
Garnets can be reused about 35 times keeping their overall properties intact. Finally, these recycled garnets degrade to an extent where they cannot be further reutilized for abrasive discharge. Then, they are taken away from the shipyards and designated as spent garnet . Recently, it is recognized that the exploitation of these spent garnets as replacement for fine aggregates in SCGPC may open up new avenue towards the realization of alternative construction materials to the conventional Portland cement (PC) based concrete. Universally, PC due to its good mechanical properties, approximately low cost, easy availability and good durability is the most commonly applied binder for the manufacture of construction materials. Thus, PC concrete is preferable in diversified applications . Nonetheless, the production of PC has some main obstacle such as the depletion of natural habitats, manufacturing of fossil fuels, and huge amount of CO2 which is released and other greenhouse gases unless inhibited. To surmount these limitations, many dedicated efforts are made to search for efficient alternative method such as alkali-activated materials (AAMs) (often interpreted as geopolymer) .
It is realized that the spent garnets may be advantageous for sustainable development compared to PC (the principal binder) upon their usage as a partial precursor substance. Additionally, based on the implemented raw minerals and alkaline substances, the final outcome displays improved characteristics than PC concrete. Some of the modified properties include low heat of hydration, swift development of early strength, formation of strong aggregatesmatrix boundary, low thermal conductivity, high resistance against acid and fire attack . Generally, alkali activated materials are classified in two categories: (a) a high calcium system with usual precursor such as GGBFS, where the primary chemical product is the C-A-S-H type gel, (b) raw materials with low Ca substance, Class F fly ash (FA) and metakaolin wherein the main reaction product is the 3D-network based N-A-S-H type gel .
Categorically, self-compacting concretes (SCCs) flow that under their own weight without requiring any external vibration for compaction has revolutionized the concrete placement. SCC was first introduced in the late 1980s by Japanese researchers. It was asserted that being an extremely practicable concrete, SSC can stream throughout constrained segments with no separation or flow . Comparatively lower yield of these concretes ensures their elevated flow capacity, modest viscosity to stand firm against separation and bleed. On the top, they must retain the homogeneity throughout transport, insertion and cure to guarantee a sufficient structural feat and endurance.
Despite many researches toward sand replacements for concrete infrastructures exploitation of spent garnet waste as construction material product is seldom focussed. Considering these notable engineering properties of spent garnet waste we explore the feasibility of incorporating different levels of spent garnet as a replacement for river sand to achieve an enhanced SCGPCs. Synthesized SCGPC specimens are thoroughly characterized to determine their compressive, flexural, splitting tensile strengths, durability and workability as a function of varying percentages of spent garnet inclusion.
In this study, the spent garnet was obtained from southern Johor (Malaysia). These heavy minerals sand being the category of ore deposits remain the main source of rare-earth building blocks and engineering minerals. Such ore deposits are typically appeared in beaches according to their contents involving the minerals specific gravity . Total heavy mineral (THM) components typically contain 150% of Zircon, 1060% of Ilmenite, 525% of Rutile and 110% of Leucoxene . The remaining bulk
Table 4 summarizes the mix ratios design in consistent with the particularization of the British Standards and EFNARC guidelines. The binder devoid of cement was prepared utilizing GBFS obtained from Ipoh (Malaysia). The coarse aggregates were grounded granite minerals with a highest size of 10mm and a specific gravity of 2.66 in saturated surface-dry (SSD) states. In geopolymer synthesis, the nature of alkaline solution decides the dissolution of silica and alumina present in the source
Table 5 provides the fresh properties of the prepared SCGPC specimens obtained using slump flow test, L-box test, and V-funnel test. The mix sample TR0 was selected as control sample whereas the TR1, TR2, TR3 and TR4 specimens were chosen as the spent garnet samples. The quantitative and qualitative analysis indicated that all the concrete mixes achieved the desired fresh properties which conformed to the EFNARC limits of SCGC . Slump flow, T50, L-box test and V-funnel values (Table 5) of
This paper reports the feasibility of using spent garnets at high percentage level as sand replacement to achieve enhanced SCGPCs for economic and environmental friendly applications. The SCGPC specimens were prepared using GGBFS where spent garnet was used to replace the river sand. The effects of varying spent garnet contents on the fresh properties of prepared SCGPCs were determined. Performance of the proposed SCGPCs was evaluated in terms of compressive, flexural, splitting tensile
This study was funded by Malaysian Ministry of Education (MOE) and UTM. Grant no. GUP/RU 12H42 and 13H50. The facilities and materials provided by Malaysian Marine and Heavy Engineering (MMHE) Sdn. Bhd are greatly appreciated.
Cold mix asphalt (CMA) is an eco-friendly sustainable asphalt mixture, mostly for asphalt surface treatments (ASTs). However, material compatibility and poor adhesion leading to high voids, moisture damage susceptibility, and weak early strength remain challenging. Efforts to solve this limitation is beamed towards binder improvement and modification with modifiers, adhesion promoters, or polymers. Other forms of AST mixture improvement entail supplementary cementitious reinforcing or pozzolanic agents in the form of by-products. In this study, the physio-mechanical and microstructural desirability of spent garnet for use as fine aggregate in CMA was explored. Spent garnet is a by-product of abrasive blasting, often produced in large quantities and disposed of in landfills. Often, spent garnet waste gets contaminated with toxic elements either during usage or in landfills. This study aimed to investigate the properties of Automatically (AG) and Manually generated (MG) spent garnet grades. The physio-mechanical, morphologic, and chemical parameters of spent garnet were assessed to achieve this aim. The result compared with relevant specifications on cold mixtures plus Jabatan Kerja Raya (JKR) requirement. Moreover, crystallinity and composition were studied using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and X-ray Fluorescence (XRF). The presence of toxic heavy metals that often contaminate spent garnet deposits in landfills was evaluated too. Results suggested that both AG and MGs high sand equivalent and least water absorption of 98 %, 89 %, and 0.14 %, 0.23 % accordingly, and can replace sand in CMA. However, MG spent garnet is not desirable for chemically sensitive materials. The AG garnet was found to be Pyrope while the MG spent garnet is largely Almandine garnet the strongest form of garnet, including traces of other garnet forms.
Steel fibers are an inseparable part of ultra high performance concretes (UHPC). The effects of steel fibers have been widely studied in recent years; however, the hybridization of steel fiber with different types of fibers and their effect on the properties of UHPC has not been completely investigated. In addition, under thermal treatment, which is a common way for curing UHPC elements, the use of hybrid fibers may change the concrete characteristics. In this paper, mixtures containing different types of fibers in the hybrid forms were produced and the specimens were cured under normal and heat curing conditions. To characterize the effect of hybrid fibers on UHPC mixes under different curing regimes, the workability, compressive strength, flexural parameters (including first crack strength, module of rupture, load-deflection curves and toughness index) and scanning electron microscope (SEM) microstructural analyses were investigated. The results revealed that the concrete mix with 2.5 % mono fiber had higher flexural performance than the hybrid mixes. However, the use of steel fiber with the volume fraction of 1.5 % was more effective in improving the compressive strength. Higher flexural load-bearing capacity was observed for the hybrid mixes with macro fibers of Barchip and Kortta. The UHP-FRCs containing Barchip and Kortta fibers, due to the permeable internal structure, had lower chloride resistance than the 2.5 % of steel fiber concrete. In addition, the chloride migration coefficients of the hybrid mixtures with the glass, carbon and polypropylene fibers were about 5 times higher than those of the mix with 1.5 % steel fiber. Compared with normal curing condition, the load drop after cracking was more visible for the mixes cured under heat curing, which could be limited by using high-volume steel fiber and hybrid micro fibers. Furthermore, applying thermal treatment for curing concrete mixes led to lower chloride ion penetration; the enhancement was more pronounced for the hybrid mixes with micro fibers of glass, carbon and polypropylene.
The drive towards sustainable construction materials that will reduce the amount of CO2 produced during the manufacture of Portland cement has led researchers to investigate the suitability of alternative materials in concrete production. The use of industrial and agricultural by-products such as fly ash, slag, rice husk ash, and natural pozzolanas high in aluminosilicate content have been found useful in the production of geopolymer concrete which has become a suitable replacement for OPC concrete with its higher strength, temperature stability, denser microstructure, higher bond strength, and resistance to chemicals. A holistic approach for the first scientometric review on geopolymer concrete is described in this study. The study embraced an all-inclusive review concept using scientometric analysis and science mapping technology, and comprehensive discussion to highlight the most influential publication sources, most used keywords, most active researchers and institutions, as well as literature with the highest impact on the field of Geopolymer concrete; to examine the current state-of-the-art research focus, and to identify the current research gaps. The study analyzed 2011 related bibliographic data mined from the Scopus database. The research gaps identified were in the areas of geopolymer type, materials, mix design, mechanical properties, durability properties, microstructure, and adoption and application. Further long-term studies are required in these areas to provide a basis for a regulatory framework for adoption of geopolymer concrete. This study will help researchers understand the current trend in geopolymer concrete, opening more room for further research as well as serve as a source of information for policy makers, journal editors, professionals and research institutions.
Ground granulated blast furnace slag (GGBFS) and copper slag (CS) are industrial waste by-products, which are mostly discarded in landfills. Alternatively, they can be used in concrete production to reduce the consumption of cement and natural aggregates. One of the applications that can benefit from heavy-weight aggregates such as CS, is concrete tailored for radiation shielding purposes. However, there was no prior study on effect of combined use of CS and GGBFS on radiation shielding capability of concrete. This study is aimed to address the effect of GGBFS and CS content on gamma-ray shielding and mechanical performance of high-density concrete. For this purpose, concrete mixes were prepared with different percentages of GGBFS (060%) and CS (0100%) as a partial replacement of cement and natural fine aggregate, respectively. The workability, compressive strength, splitting tensile strength, and radiation shielding capability of concrete mixes subjected to 137Cs and 60Co point sources were evaluated. Based on the test results, the workability of fresh concrete was enhanced (up to 63%) with increasing replacement ratios of GGBFS and CS. The optimum compressive and splitting tensile strengths were obtained by incorporating 30% GGBFS and 50% CS, which were about 20% higher than that of the control mix. The linear attenuation coefficient increased slightly with GGBFS content. On the other hand, the use of heavyweight CS aggregates increased the linear attenuation coefficient by up to 31%. Results showed that concrete made with 60% GGBFS and 100% CS exhibit superior radiation shielding capability and satisfies the strength requirements for structural applications. Therefore, it is suitable for radiation shielding of structures such as healthcare centers. Finally, the ecological analysis revealed that the concrete made with recycled materials is Eco-friendlier and contributes to sustainable development of construction industry.
This article investigated the feasibility to synthesise geopolymer bricks from Granulated Blast Furnace Slag (GBFS) using alkaline activators without addition of sodium silicate or silica reactive source. Sodium hydroxide (NaOH) is a typical alkaline solution used in geopolymerisation compared to KOH with addition of silicate solution used as a catalyst to enhance the dissolution process. However, a comparative study between the two alkaline activators in the absence of silica solution are very scarce and limited. For this purpose, this article investigated the effect of type of alkali (NaOH and KOH) on unconfined compressive strength (UCS) with the aim to establish the best alkali activator that possess high activation potential and favours GBFS geopolymerisation. In addition, the effect of alkali concentration, liquidsolid ratio, curing temperature and time on the physical and mechanical properties of geopolymer bricks were investigated using UCS, SEM micrographs, XRD analysis, water absorption, and bulk density. Metal leachability and durability of the synthesised geopolymer brick was also investigated. The results show that geopolymer brick prepared with NaOH favours GBFS geopolymerisation. The optimum curing conditions that yielded the highest UCS of 72MPa were 15M NaOH, liquid to Solid ratio of 0,15, curing temperature and time of 80C and 5days. The highest UCS was due to formation of a dense, less porous and more amorphous microstructure. The synthesised geopolymer brick met the minimum required UCS and the water absorption % to be used as facing and solid mansory brick in accordance with ASTM C126-99 and ASTM C216-07a respectively.
Geopolymers are inorganic materials that result from the alkali activation of aluminosilicates. The aluminosilicates source materials can either occur naturally (e.g. kaolin, metakaolin, rice husk ash, volcanic rock powders) or are produced by industrial processes (e.g. fly-ash, blast furnace slag). While the potential application of geopolymers as construction materials (e.g. concrete manufacturing and soil stabilization) has been studied in the past, their widespread use has been limited. This is mainly because the technology is still relatively new and research in this field is still emerging. However, the use of geopolymers in lieu of conventional binders (e.g. cement and lime) has substantial environmental advantages particularly in terms of the energy expended for their production and greenhouse gas emissions. The current trend to enhance sustainability practices in the construction industry has recently driven research in this area. This paper aims to offer a comprehensive overview of past studies on geopolymers synthesised from various precursors, the factors affecting geopolymerisation process, their microstructural characteristics as well as mechanical, chemical, thermal and environmental properties of geopolymers. Further, recent developments associated with the use of geopolymers as construction materials in civil engineering applications have also been discussed. Research findings show that geopolymers can achieve comparable or superior performance to conventional binders and/or concrete in terms of shear strength and durability but with a reduced environmental footprint.
The use of recycled aggregate concrete (from construction and demolition wastes) in buildings has the advantage of being more environmentally-friendly. However, this type of concrete has lower mechanical performance, namely in terms of modulus of elasticity. This lower value has influence on columns second order effects. For this reason, a numerical sensitivity analysis was carried out to study the influence of second order effects on safety of recycled aggregate concrete columns. Two different Eurocode 2 methods were used for this comparison: a method based on nominal curvature and a method based on nominal stiffness. The results were obtained for different slenderness values and axial force levels, for the same initial percentage of reinforcing steel area, which was determined to guarantee the structural safety due to first order effects only. The obtained results show an increase of reinforcement area in columns built with recycled aggregate concrete, when compared to natural aggregate concrete, due to second order effects.
This study uses finite element analysis to compare the performance of load-bearing wooden-frame panels in terms of connection displacements caused by lateral loads resulting from soft-body impacts and wall's parallel load resulting from suspended objects. The panels were designed based on the project concepts of the Design for Sustainability and the Design for Reuse. Connections play an important role in the design of the panels as they support and transmit loads to contiguous panels without collapsing. We designed two panels and connected them using an aluminum alloy (H-shaped cross-section, 2.0-mm thickness). An instantaneous impact energy load was replaced by an instantaneous equivalent load. Afterwards, the simulation was repeated for long-term loading during 24-h to verify the creep effect. The results obtained showed that all the simulations performed herein meet the standard prerequisites and the wall thickness could be less than used in this analysis. Yet, for constructive facilities and thermal and acoustic behavior, the thickness remained unaltered to improve these properties, regarding other studies previously developed.
Influence of natural additives on mechanical and physical properties of hydraulic lime mortar has been investigated experimentally. Results revealed that organically modified lime mortar enhances the compressive strength significantly as it improved the bond between two consecutive lime particles in the matrix. Results also reflected that organically modified lime mortar with longer curing periods increased the compressive strength compared to reference mortar made of lime without organic addition. It is due to the presence of proteins and carbohydrates in the organic additives that influences the carbonation and hydraulic reaction in the lime matrix which helps to enhance the compressive strength of modified mortar. Addition of organic additives in lime mortar also reduces the porosity in the matrix and increases the hydrophobic nature and reduces water affinity of the hydraulic lime mortar.
The enhancement in the mechanical properties of high strength lightweight concrete (HSLWC) utilizing palm oil clinker (POC) as a replacement for oil palm shell (OPS) as lightweight coarse aggregate has been investigated and reported. A series of concrete mixes was prepared with 25%, 50%, 75% and 100% replacement of coarse aggregate by POC in HSLWC, while setting other parameters as constant. The parameters investigated include slump value, compressive strength, stress-strain behaviour, modulus of elasticity and its normalization, ultrasonic pulse velocity (UPV) and failure modes. The results showed that the replacement of OPS by POC as coarse aggregate has significant positive impact on compressive strength, modulus of elasticity and UPV. The highest compressive strength of about 63MPa obtained for the mix with POC was about 43% higher than the control mix. Moreover, the enhancement in modulus of elasticity up to 2.5 times could significantly control the deflection.
Nowadays, geopolymer with alkali activation binders are introduced as alternative environmentally friendly construction materials to the ordinary Portland cement for solving the carbon dioxide emission and high energy consumption problems. In the construction sectors worldwide, the durability of concrete is the major concern. Concretes produced by recycling the agricultural and industrial wastes were shown to be environmentally friendly with improved durability performance. In this view, present paper examines the effects of fly ash (FA) as replacement agent to GBFS on the durability performance of synthesized self-compact alkali-activated concrete (SCAACs). Six concrete mixes each with a different percentage of FA (30, 40, 50, 60 and 70%) in place of GBFS were designed. A control mixture with 100% GBFS content was used as base specimen to compare other five mixes. Properties such as filling and passing ability, compressive strength, drying shrinkage, carbonation depth and resistance to sulfuric acid were measured. The life cycle of proposed SCAACs were assessed in terms of CO2 emission, cost and saving energy. The resilience and the workability of the SCAAC mixtures were improved when FA was substituted with GBFS at 40%, 50% and 60%. Addition of FA could largely enhance the SCAACs durability and exhibit superior performance against sulphuric acid attack. Likewise, concrete mixtures containing FA of 50% and above showed reduction in CO2 emission over 20%, cost about 15% as well as energy consumption almost 18%. It was concluded that by substituting GBFS by FA a potential solution to the issue of trying to reduce CO2 emission and contribution to a healthier environment can be achieved.
The presence of alunimosilicate based fine aggregates (2.5 to 7.5wt%) effectively acted to densify the microstructure of the interfacial zone with a reduction of pore threshold and mean pore size jointly with change on the fracture mode of the Self-Compacting (SC) geopolymer concretes. From the results, pumice and recycled glass with amorphous structure improved the bi-axial four-point flexural strength from 5 to 8MPa while semi-crystalline feldspar sludge (nepheline syenite) reached 11MPa. The formation of additional geopolymer gels were responsible for the strengthening mechanism. The specimens with amorphous fines showed the tendency to delay the desorption in the laboratory conditions indicating the need for a very long curing time for the final consolidation. The semi-crystalline fines -nepheline syenite- appeared appropriate for the design of self-compacting geopolymer concretes due to their bulk composition, capacity to enhance densification and strength with low deformation rate, in a short range of curing together with a high rate of desorption, all important parameters for the prediction of the durability of concretes.
Water jet Garnet is a non-toxic natural substance that can be recycled for recycle. Usually, the used water jet garnet can be disposed to landfills. Some garnet suppliers offer recycle garnet services.
For many first-time owners of abrasive waterjet systems, the question of whether they will be dealing with hazardous waste in either the abrasive or the water looms large. Companies dont want to expose themselves to huge disposal or treatment costs, or face fines or litigation.
Because of the numerous levels of government in the U.S. and all of the materials a waterjet can cut, shops should keep abreast of current local solid-waste and water disposal regulationsand know the business and environmental costs of what theyre throwing away.
The toxicity characteristic leaching procedure (TCLP), a key test for used water and abrasive, determines the toxicity of waste. Developed by the EPA, the TCLP simulates the leaching waste undergoes if its disposed of in a sanitary landfill. It essentially determines how much, if any, of the toxicity characteristics will leach from the waste and enter the environment. If you will be purchasing a water softener, reverse-osmosis system, or water recycling system, the equipment supplier also should be willing to provide this testing service to you at little or no cost. For abrasive, ask your waste hauler whom it uses for TCLP. Your waste hauler performs this test at least once a year anyway.
While less than 5 percent of waterjet users might be at risk of putting hazardous waste down their drain, it is worthwhile to verify that you are in the 95 percent group, said John Frosheiser, president of Custom Service and Design, a filtration supplier in Auburn Hills, Mich. If you are in the 5 percent minority, it is important to know that there are ways to protect your companys interests.
First, get your water tested, and ask your local water utility for a listing of limits for heavy metals. You can either check out the utilitys Web site or simply call. Research about local practices is paramount, because the rules can change from municipality to municipality.
Now comes the chicken-and-the-egg problem: If you are a first-time waterjet user, you have no water to test before buying a system. You may have an idea of what materials you might be cutting, but certainly not the entire universe of materials, especially if you run a job shop. In this situation, try to take a sample of water from your waterjet supplier when you are having production cuts done. Simply gather a sampling of the overflow water and have it tested. If you find that you are near or above local limits, you have a number of options, such as filtering the water before it goes down the drain.
With waterjet cutting, you are pulverizing the cut material and not structurally changing the material like with electrical discharge machining (EDM). Therefore, most of the impurities in waterjet overflow water are suspended solids, not dissolved.
Because waterjet cutting doesnt leach material like EDM, installing a simple settling tank prior to the drain is the oldest and best form of filtration, said Frosheiser. For most, this is enough to get the water within acceptable limits.
Settling tanks also help keep sewer lines clear. Over time enough suspended solids can settle out from your wastewater to block or restrict the sewer lines. If the municipality traces this back to you, you could face a large cost to cover the cleaning of the lines. So, be a good neighbor and put a settling tank inline. They are inexpensive to build or buy and simple to maintain.
If you are still uncomfortable with what you are putting down the drain, a closed-loop water recycling system may give you peace of mind. In some localities, it is the only solution. Such a system uses a series of filters to clean the overflow water from the waterjet. After going through the system, the water is pure enough to be sent back to the high-pressure pump for reuse in the waterjet process.
Garnet, the typical waterjet abrasive, is an inert, naturally occurring, semiprecious mineral It is either mined out of the mountains of upstate New York or Idaho, or shoveled off of beaches in Australia or India. Abrasive suppliers have material safety data sheets (MSDS) for garnet that typically can be downloaded from their Web sites.
If you are cutting lead or beryllium copper, then you may have a hazardous waste situation, said Alan Bennett, market manager for garnet supplier Barton Mines Co., Glen Falls, N.Y. For most other materials, the amount of the scrap material in the abrasive is so small that it is rarely a problem. Even most stainless steels are usually not an issue unless they contain a high nickel or chrome content.
Because of the density of abrasive, reducing transportation distance is vital to reducing this cost, said Bennett. The shorter the distance your waste needs to be hauled, the lower your cost will be.
Behind many waterjet job shops sit several bulk bags of used abrasive piled up, draining water. Theyre draining as much water as possible from the abrasive so they dont have to pay for the disposal of water as well. Alternatively, a shop can invest in abrasive removal systems that drain off most of the water from the abrasive while it is being removed from the waterjet catcher tank.
Abrasive recycling may be another option depending on how much abrasive you use. Recycling systems can be costly to run and maintain, so this must be balanced against the savings. Some claim anecdotally that they actually get faster cutting speeds with recycled abrasive because it has been crushed during the cutting process, in essence giving each particle a sharp edge.
As just one example, some municipalities may allow your abrasive to be classified as a byproduct rather than waste and give you a lower rate for hauling it away. Being a good environmental citizenknowing that what youre throwing away is environmentally safeis important enough. But without knowing local regulations like this, youre leaving money on the table.
Sandblasting is used to clean dirt, corrosion, paint or other coatings from a variety of surfaces. The clean grit should in most cases contain no hazardous properties. Common industries where sandblasting is applied include shipbuilding and maintenance, transportation bridge maintenance, and military operations. Abrasive blasting has been a concern for a number of years in regard to worker safety during the blasting process. Issues of concern include worker exposure to silica dust, extreme noise exposure, and mechanical and electrical hazards (NIOSH, 1976). An issue of less noticeable concern is the disposal of the used ABM. In light of stringent waste management regulations and heightened awareness of environmental contamination, additional focus has been placed on the management of this waste stream.
The problem presented with the used abrasive blast media is that it may contain materials from the cleaned surface which impart hazardous characteristics to the grit. Sandblasting is often used to remove paint from metal and other surfaces. Surface coatings with paint are often necessary to protect from deterioration in the environment, most notably the marine environment (ships and bridges are the prime example). These paints usually contain heavy metals which act as anti-fouling and anti-corrosion agents. When the metal surfaces are cleaned as part of routine maintenance and repainted, the metals in the paint become part of the waste ABM matrix. And indeed, heavy metals are the most common contaminants of ABM waste. The contamination of the abrasive results in potential restriction for disposal and recycling (Ovenden, 1990).
Although no specific regulations are in place for used sandblast grit waste, it is a solid waste, and as with any non-excluded solid waste the generator of the waste is responsible for determining if the waste possesses hazardous characteristics, and is thus a hazardous waste. This is therefore a necessary step in determining the disposal and reuse options available. Environmental regulations require that a Toxicity Characteristic Leaching Procedure (TCLP) test be performed to determine if the material is hazardous. If it is hazardous, the material must be managed accordingly. If not determined hazardous, the grit is a solid waste which must be disposed of properly.
There are many types of abrasive blasting media available. Sand is one of the most common blasting materials. Sand is the least expensive non-reusable media. Alternatives to sand abrasives include other mineral sands with no free silica, metal slag, and coal slag. Coal slag has been used frequently as a blasting material. Media of these types may not be reused in the abrasive process, but can be recycled into other materials (e.g. cement or concrete). Types of abrasive blasting media which are used more than one time include garnet, steel shot, and glass bead. These media may be screened and separated after used to capture reusable particles. Plastic blast media is reusable and versatile. It can be used in circumstances when harder materials may be too damaging to sensitive surfaces. One such application is the surface of jets and planes. Spent plastic media may also be recycled into other materials such as counter tops. Other materials which have been used as blasting materials include walnut shells, impregnated sponge, and dry ice.
One problem with the management of this waste stream is that it has often times gone unnoticed as a solid waste and the need for testing for hazardous characteristics has not been recognized. This results in part from the physical appearance of the waste. When silica sand has been used, the waste very much looks like sand and is therefore not easily recognized by some as a solid waste. This material would be simply spread around the property and treated as additional soil. As new safety regulations resulted in different types of ABM being used, the residue from these materials was more noticeable as a solid waste. An example of this is coal slag, which although is similar in physical character to sand, is black in color. Used ABM is also more recognizable than in the past because safety regulations often require the ABM to be contained and not used in open atmosphere conditions. This has resulted in waste that is now collected, which in the past was perhaps left to make its way into the environment.
When surveying Florida regulatory data for this search, there was not a large amount of information was found. Toxicity Characteristic Leaching Procedure (TCLP) tests performed for larger projects in the state, and total metals concentration for a few also, but little of this data has been correlated. Enough data was collected, however, to make a few generalizations. For the most part, the waste ABM surveyed for this report was non-hazardous (only 3% was hazardous). However, the heavy metal content of the waste was still large enough to limit recycling and disposal options. Lead and Arsenic were the two metals encountered which exceeded the risk-based standards set by EPA and FDEP the most. Question still remain regarding the true leachability of the heavy metals to the environment. The typical data encountered in the regulatory files did not perform leaching tests to determine possible groundwater input, but rather to test for hazardous characteristics.
The challenges of managing this waste stream stem from the fact that it is generally not hazardous, its appearance is soil-like, and disposal and reuse options are not always clearly outlined to either the regulators or the industry. Nonhazardous sandblast grit waste still needs to be disposed of in a sanitary landfill. A lined MSW landfill is normally considered to be the requirement but the possibility of using construction and demolition waste landfills has been raised by generators.
A number of recycling options are possible for the management of ABM. Spent blasting abrasives have been used as a feedstock material in the production of Portland Cement. (Salt et al. 1994, Brabrand and Loehr 1993) This recycling option is currently practiced by the Tampa Port Authority, along with three cement kilns throughout the state of Florida. Used ABM also has the potential to be used as aggregate in the production of Portland cement concrete and in the production of asphalt concrete for roadways. In such cases the material not only has to meet state and federal regulatory disposal questions, but would also has to meet the physical and chemical requirements of the manufacturing process. Other options for recycling include recovering some fraction of ABM for reuse, using as a clean fill material (if clean enough), and using as a drainage material in landfills or septic tanks.
The management of solid waste from abrasive blasting is an issue which will be more frequently encountered in the future. While existing guidelines and regulations are available, a single resource which spans such a wide array of information does not currently exist. Future work should concentrate on collecting and summarizing best management practices for ABM waste management in a format which could be used by the many industries which perform abrasive blasting, and the engineering and regulatory community.Get in Touch with Mechanic