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By D. Carr, C. Anderson, M. Deal, C. Larson

"Construction of the OceanaGold Haile operation’s process plant in Kershaw, South Carolina is currently under way, with ore through the mill expected in late 2016 and commercial production expected in early 2017. The process is designed to treat 6,350 tonnes per day with minor upgrades required to achieve 8,270 tonnes per day. Plant optimization during detailed engineering, combined with a focus on de-risking the process, has resulted in numerous process changes since the initial design. This paper describes the plant optimization and de-risking, it also presents a proven commissioning strategy modelled after OceanaGold’s Didipio operation, whilst identifying potential expansion opportunities. INTRODUCTION Haile Gold Mine is located in Kershaw, South Carolina, approximately 50 miles south of Charlotte, North Carolina. Gold was first discovered at the site in 1827, and the property has been through several operating periods since. The last operation employed heap leaching from 1985 through 1992. Since then, the property has been closed and fully reclaimed. Romarco Minerals acquired the property in 2007, and began an exploration program that delineated 2.02Moz. of gold in reserve at an overall grade of 2.06 g/t. OceanaGold acquired Romarco Minerals and the Haile Operation in October of 2015. OceanaGold operates under a risk management philosophy in all aspects of operation, both corporately and at each individual business unit, and has implemented numerous process changes to eliminate or mitigate risks identified in the initial design of the processing circuit, and provided increased opportunity for optimization and expansion. This paper describes the plant optimization and de-risking, it also presents a proven commissioning strategy modelled after OceanaGold’s Didipio Operation, and identifies potential expansion opportunities. INITIAL PROCESSING CIRCUIT DESIGN An extensive metallurgical test work program was undertaken by Romarco Minerals and third party laboratories during the initial design phase of the Haile project [1]. This preliminary test work provided the technical information as a basis of plant design. The initial flow sheet for the Haile processing circuit is shown in Figure 1 (see APPENDIX). The plant is designed to process 6,350 tpd (7,000 stpd) on an annualized basis. The process begins with a jaw crusher followed by a SAG and ball mill grinding circuit to reduce particle size to P80 74 µm. A flash flotation cell treats 50% of the cyclone underflow in the ball mill circuit. Grinding circuit product is sent to a rougher flotation circuit to recover gold-bearing pyrite. The flotation concentrates from flash and rougher flotation are reground to P80 13 µm using stirred media detritors (SMD’s). The rougher flotation tail is pumped to the carbon-in-leach (CIL) circuit for gold recovery. The reground concentrate is pre-aerated prior to being pumped to the CIL circuit. The CIL circuit is a hybrid circuit with eight tanks. Tank 1 leaches the pre-aerated concentrate only, and tanks 2 through 8 leach the combined flotation tailing and tank 1 discharge. The carbon strip circuit is a standard pressure Zadra system, followed by electrowinning, and refining using an induction furnace. CIL tailing passes through a cyanide recovery thickener prior cyanide destruction and then pumped to the tailing storage facility (TSF)."

Jan 1, 2017

By B. T. Darnton

Gravity concentration at the Pegasus Gold Montana Tunnels Mine was initiated in late June, 1991 with the commissioning of a coarse gold scalping circuit that processes a small portion of the ball mill circulating load. The primary objective for the circuit was to reduce the risk of gold particles advancing to flotation that are too coarse to float. The secondary objective was to enhance overall gold recovery and payable gold ounces in a cost effective manner. The gravity circuit has proven itself to be a major success. The above mentioned goals have been achieved, and they have been maintained at record throughput rates that are 30% higher than when the circuit was commissioned. A number of modifications and improvements were made over the last three years which allowed the gravity circuit to keep pace with the higher tonnage, these are discussed in detail in the body of this paper. The overall approach to gravity concentration at Montana Tunnels has always been to optimize production rather than maximize the gold ounces produced. This philosophy has now yielded a circuit expansion and relocation project which will allow for an estimated 50% increase in gravity gold production, while reducing the overall unit costs of production significantly. This paper will review historical gravity circuit performance, improvements, and the current relocation and expansion project.

Jan 1, 1995

Production targets are the basis for almost every decision made by operations personnel in the daily operation of a concentrator. It is the production targets that determine how the plant is operated and therefore determine its efficiency. However, to achieve maximum plant efficiency production targets must be relevant to the process and achievable.In RoseberyÆs case, for many years, production targets were taken from budget data which, with the exception of mill feed tonnes and grades were carried forward from the previous budget. The zinc concentrate grade target was fixed at 57 per cent Zn, a long-term average; it was the accepted æstandardÆ for Rosebery. Historical data showed this target was never consistently achieved and plant efficiency was highly variable.Investigations into the possible causes for the variable performance ruled out plant and mechanical issues. Despite the Rosebery concentratorÆs age the plant and equipment are more than serviceable and reliable. The mineralogy of the ore and specifically the iron content of the sphalerite was found to be the most significant determinant of zinc concentrate grade. It was found with increasing frequency that the zinc grade of the sphalerite in the ore was below the zinc concentrate grade target. Consequently on these occasions attempts to meet the required concentrate target destabilised the process resulting in plant inefficiencies.Using the correlation between iron and zinc, data modelling was able to accurately predict the maximum zinc concentrate grade achievable for any ore type. By using on stream analysis instrumentation the operations personnel are now provided with constantly updated concentrate grade targets. By knowing the mineralogical limits of the ore at the time it is being treated process stability is maintained allowing plant efficiency to be optimised. This has resulted in a step change in plant performance and a significant increase in revenue.CITATION:Harris, G R, 2012. Developing and implementing ore-specific targets for the Rosebery Concentrator, in Proceedings 11th AusIMM Mill OperatorsÆ Conference, pp 321-324 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 29, 2012

By N. Moony

The benefit of gravity separation in improving total gold recovery in grinding circuits has been outlined in a significant number of papers to date. However, the use of batch centrifugal concentrators (BCC) as an industry standard to extract gold has limited the potential for maximizing gravity recoveries -particularly in coarse gold deposits. This is a reflection of the high upgrade ratios obtained by BCC's which has an inverse relationship with recoveries. Survey work in Australia has indicated that installation of the InLine Pressure Jig as an alternative to the Bee will significantly increase recoveries of gold by gravity and, accordingly, increase total gold recoveries and lower operating costs.

Jan 1, 1998

By Ram V. Ramachandran

As an industry with major potential impacts (both good and bad) on water resources and due to the rising costs of process water, the mining and metallurgical processing industry has a key responsibility to contribute to the overall goal of preserving both the quantity and quality of water available within the watersheds they operate in. As we plan for new and existing mining and metallurgical projects, we need to consider a hierarchy of options to minimize our impact within the watersheds we operate; keeping clean water clean by diverting around our operations; reduction in the amount of water we use; reuse of water wherever possible, and improvements to water quality for recycling and/or release to environment. Technology is needed to treat water to improve its quality for reuse or release to the original watershed. While lime precipitation followed by sulfide polishing is effective for removal of most of the metals, it does little or nothing to remove ammonium ions and anions such as chloride, nitrate, molybdate, arsenate and selenite/selenite. Regulations on sulfate limits in treated discharge water has drawn close attention to the treatment of acid mine drainage (AMD). Management of brine and salt disposal is also posing a problem due to strict regulations and cost of disposal. This paper will: (a) address issues associated with managing water with the objective of maintaining water sheds—status quo-during and after operation (b) discuss potential technologies for advanced water treatment plants.

By Brian Hart, Rong Fan, Roger Smart, Andrea Gerson, Ning Xu

A complete strategy has been developed for identification of the reasons for losses in recovery and/or grade, due to changes or complications in mineralogy and in mineral surface conditioning, and their subsequent correction. The sequence of methods starts with comparison of mineral phases between QEMSCAN/MLA (compositional) and Rietveld XRD (crystalline diffraction) with bulk assay reconciliation. This methodology has recently led to identification of unrecognised amorphous content (12-40 wt.%), previously attributed to crystalline phases, in the fine fraction (<35 µm) of some problematic flotation feeds. Attached amorphous silica, talc- and chlorite-like fines have direct influence on the hydrophobic/ hydrophilic ratio on value mineral surfaces adversely affecting flotation. SEM/EDS is used in the backscattered imaging mode to determine possible problems with liberation (e.g. remnant local locking), not detected in standard liberation analysis, resulting in gangue flotation. EDTA extraction is used to assess bulk feed pre-oxidation and sequential oxidation product loading through the circuit. Changes in circuit solutions are assayed with speciation modelling of precipitates and potentially adsorbing species. ToF-SIMS with principal component analysis is then used to correlate surface species with specific minerals and can be used to assess the effectiveness of specific reagents particularly collectors. This approach identifies unwanted activating species and interference with value surfaces by adsorbed hydrophilic ions, precipitates and fine particles. When the interference or ineffective reagents are specifically identified, remedial action can be targeted. This method has identified residual talc-like layers (<10 nm thick) inducing gangue flotation of pyroxene and chromite in PGM flotation. Recent case studies of application of the full methodology to losses of molybdenite at KUCC and to sphalerite activation in the Cu/Pb circuit at Brunswick Mines with remedial action are discussed.

Jan 1, 2014

By George C. Toland

Most existing impoundment ponds and dams leak effluent into the soil or rock upon which they are constructed. However, proposed environmental legislation will require very stringent control on the release of toxic effluents such as cyanide. More exacting investigation, design, and construction techniques than have been used in the past will be required to satisfy these new regulations. This paper discusses the types of field and laboratory investigations required to develop the data for the design of an impoundment system containing toxic effluent, and discusses in detail technical considerations necessary to design this system. Design topics include reservoir sealing with natural and man-made materials; embankment sealing; embankment design considering stability, surface hydrology, capacity, and downstream catchment basins; and special implications of cyanide effluents.

Jan 1, 1975

By W. Petruk

Mineralogical studies and concentration tests were conducted on samples from an oolitic iron deposit from the Peace River district in Alberta to determine what concentrate grades and metal recoveries could be obtained. The samples assayed 32 to 37 wt. % Fe, and consisted of goethite, nontronite, ferruginous opal, siderite , quartz, amorphous phosphate and illite . Flotation with fatty acids yielded the best over-all results. A flotation concentrate from a composite sample of the iron horizon assayed, by weight, 43.0% Fe, 12.3% SiO2 , 1.9% CaD, 0.9% MgO, 4.5% Al2O3 and 2.0% P2O5 and lost 17.2% on ignition, for an iron recovery of 48.8% and a silica rejection of 80%. When heated to drive off the water, the concentrate assayed 52 w t. % Fe and 14. 8% w t. % SiO2

Jan 1, 1977

By E. D. Gardner

Humphreys Gold Corporation of Denver, Colo., was conducting a successful placer operation in 1936 on North Clear Creek about 6 miles below Blackhawk in Gilpin County, Colo. About 3,000 cubic yards of gold-bearing gravel are dug daily (September. 1936) by two draglines and a power shovel. The gravel is screened in a portable washing plant; the trommel oversize is discarded, and the undersize is pumped to a gold-saving plant. The gold is caught in riffles in sluice boxes. The total cost of mining is about 20 cents per cubic yard. The mine is in a narrow canyon at an altitude of 7,200 feet. The Blackhawk-Central City branch of the Colorado & Southern RR. runs over the property. Freight platforms for receiving supplies were moved as the workings advanced. The workmen reached the mine on a speeder that ran on the railroad tracks from a point on the automobile highway (U. S. 40) on Clear Creek near the bottom of Floyd Hill, about 5 miles distant. The mine is 36 miles by road and speeder, or 30 miles by rail, from Denver.

Jan 1, 1937

By L. M. Lowe, D. B. Chambers, D. G. Feasby

"The presence of the naturally occurring radioactive elements uranium and thorium in rare earth (RE) resources can present challenges in achieving regulatory and social acceptance. The discovery and awareness of radioactivity in mineral resources radioactivity typically generates strong public intuitive responses that may be project prohibitive; a significant proportion of such resources contain radioactivity.The objectives of this paper are to demystify the presence of uranium and thorium in RE resources and to demonstrate how a RE project can be safely developed, operated and closed from a radiological perspective. Radioactivity in RE resources is principally thorium-based. Thorium is interesting and challenging from a metallurgical perspective – one of those stubborn metals commonly assessed as refractory. Thorium is difficult to mobilise into solution and easily precipitates out. Thorium is a common element in the earth’s crust – about 10 ppm on average, and natural geophysical systems conclusively demonstrate its immobility. Specific mine tailings contain elevated levels of thorium, but the contained thorium is neither a significant ecological nor a personal hazard.Waste management for a hard rock rare earth project includes the management of mineral processtailings, waste rock, and metallurgical residue. Proven strategies are available for tailings and waste rockfor all climate conditions. The management of the metallurgical residues is potentially more challenging.Example robust strategies for addressing these challenges are presented.A potential way to reduce the radioactivity of rare earth metallurgical wastes is to selectively remove uranium and thorium. Uranium oxide is readily marketable, but its concentration as a byproduct typically triggers extensive regulatory processes. Thorium is presently not marketable, but may be so in the not-too-distant future with the development of thorium-based nuclear energy. The pro’s and con’s of uranium and thorium byproduct recovery are summarized."

Jan 1, 2016

By John C. Kleiber

From time to time since the initial installation of an experimental flotation section in 1940 (reference A), Permanente Cement Company has made efforts to beneficiate the low-grade limestone fraction which occurs in its deposit at Permanente, California, The encouraging results outlined in this paper are the result of Permanente&apos;s latest effort. This paper discusses the factors governing the selection of the flowsheet with particular reference to marketability of the sand tailing by-product. The process flow is outlined in detail, and operating statistics of the plant are presented. Finally, the problems encountered in the operation of Permanente&apos;s beneficiation plant are discussed as well as solutions sought and found.

Jan 1, 1964

By K Lee, L Mann, J Bygrave, G Sheldon

Ausmelt is supplying commercial quantities of an alkyl hydroxamate flotation collector AM28 for flotation of oxide and supergene base metal ores and tailings. AM28 is a non-hazardous product used as a ten per cent to 50 per cent solution in dilute potassium hydroxide. It is a selective flotation collector for oxide or oxidised base metal minerals and replaces conventional sulfidisation for oxide mineral flotation. At Radio Hill, the AM28 is used in conjunction with traditional sulfide collectors, which allows simultaneous flotation of oxide and sulfide copper minerals. The Fox Resources Radio Hill copper concentrator near Karratha, Western Australia, is currently configured to treat supergene copper ore sourced from the West Whundo open pit. This Archean VMS type copper deposit has been deformed and remobilised with uplift, erosion and weathering to form a significant supergene zone. The sulfide copper minerals present in the upper zone are digenite and chalcocite with lesser chalcopyrite and covellite. Oxide copper minerals present include cuprite, with lesser malachite and azurite. Gangue minerals include quartz, talc and chlorite. Plant trials at Radio Hill are reported for supergene West Whundo ore, where the AM28 was stage added into the circuit at nominally 80 g/t. Plant data over three months shows the copper recovery increased consistently from around 50 - 60 per cent to above 70 per cent when AM28 was added. This has been proven statistically. The grade of the concentrate was consistent with and without AM28, at nominally 22 - 24 per cent copper.

Jan 1, 2007

By M. J. Collins

A hydrometallurgical process has been tested at the Sherritt Research Centre for separation of zinc, lead, copper and precious metal values from the zinc oxide fume leach residue stockpiled at the HBM&S operations in Flin Flon, Manitoba. Zinc is found primarily as zinc femte and sphalerite in the residue, lead as lead sulphate and jarosite, and copper as sulphide and jarositic compounds. Gypsum and siliceous gangue are significant diluents. The separation process includes hot acid, atmospheric and reducing (sulphur dioxide) leaching; zinc, copper and lead flotation; and atmospheric iron removal steps. Zinc is recovered to a high strength zinc sulphate solution and to a zinc sulphide concentrate suitable for feed to a roaster or to a zinc pressure leach plant; lead to a high grade lead sulphate concentrate suitable for feed to a lead smelter, and copper to a high grade copper sulphide concentrate suitable for feed to a copper smelter. Precious metals are divided between the zinc, lead and copper concentrates.

Jan 1, 1993

By John E. Shelton

The growing interest in beryllium as a structural material, and its in-creased use in recent years for atomic energy application, have led both government and industry to express concern over the inadequacy of the beryllium resources in the United States and the free world. Contemplated and proposed uses for this unique material will surpass the capacity of the domestic beryllium mining industry to supply raw material, which is presently extracted from relatively small deposits by hand sorting. The need for a simple beneficiation process for beryl ores has long been recognized by the Bureau of Mines, but to date no single process has proved satisfactory for treating deposits containing a sufficient tonnage of beryl ore to warrant commercial exploitation. As a part of the Bureau&apos;s continuing effort to develop an economical recovery process, this report describes flotation research on samples of beryl-bearing pegmatites from the George Roebling mine in Connecticut, and the Colony mine in New Hampshire. The study resulted in two methods of treatment to which the ores responded reasonably well.

Jan 1, 1961

By Lewis Robert M.

The importance of phosphate in feeding the people of the world has been recognized by mining companies as they continue their search for new ore deposits and ways of improving phosphate production. An extensive phosphate-recovery research project involving investigation of beneficiation variables by batch testing, flotation pilot-plant processing of the major portion of the ore, gravity separation of the coarse fraction, and recovery of byproduct heavy minerals of a North Carolina phosphate deposit has been completed. Data obtained through batch tests enabled the development of an economical flowsheet which proved successful for the efficient recovery of a good quality phosphate concentrate in a pilot plant.

Jan 1, 1975

By Xu Wang, Yizhe Zhang, Yangge Zhu, Xiao’ou Xia, Fangming Liu

"The progress of lean magnetite preconcentration in China was introduced in this paper, such as using coarse crushing to reject tailings, and multistage grinding, multistage magnetic separation. The applications of “more crushing and less grinding” process and equipment in lean magnetite preconcentration could reduce production costs effectively. The related analysis and study on concrete cases were carried out in this paper.INTRODUCTIONIn the case of the slowdown and weak recovery in the global economy, bulk commodity prices fell sharply in 2015. Take iron ore's prices for example, about 60% grade iron ore's import prices in China from about $65 per ton at the beginning of 2015 fell to about $42 per ton in the end of the year, down by about 35%. But iron ore resources are non-renewable resources, with the continuous development and utilization of mineral resources, high grade iron ore resources will be exhausted gradually. Accompanying with the economic recovery iron ore prices after this fall is bound to return to its value to maintain a high level.The development and utilization of resources is gradually turning to the low grade iron ore. Restricted by technical development level and disadvantages of lean iron ore resources, the cost of utilization lean iron ore resources is relatively high. Making full use of their rich lean ore resources has become many countries' important strategy to get rid of dependence on foreign countries' ore. Over the years with the development and progress of lean magnetite mineral processing technology in China, the production number of concentrator has been greatly improved.As the world's largest steel producer and consumer countries, ensuring a stable and continuous supply of iron ore is particularly important for the healthy development of China's iron and steel industry. Chinese iron ore production and import data in recent years are showed in Table 1.With the expansion of iron and steel production, iron ore demand has also been a phenomenal growth. Taking 2013 for example, China's crude steel production is about 780 million tons in 2013, accounting for about half of the world's total output of crude steel. At the same time, China is also the first major iron ore import countries whose iron ore imports in 2013 was about 820 million tons, an increase of about 10%. The degree of external dependence is very high. In some years, the cost of China's iron ore imports was even more than $100 billion, and second only to oil’s import cost in all bulk commodities."

Jan 1, 2016

By H Sichani-Teimouri, B N. Noller, J C. Ng, R N. Alsaadi, P L. Breuer, S Shini

Cyanide has been used for over a century worldwide for gold extraction. However, the presence of several metals and metalloids in ore requires greater amount of cyanide for an efficient gold recovery due to their solubilisation in conjunction with gold. The extraction residues are discharged into tailing storage facilities (TSFs) and may cause bird mortality if there is exposure to cyanide-bearing wastewater exceeding the toxic threshold. The toxicity arises from free cyanide released from weak acid dissociable (WAD) cyanide complexes. The International Cyanide Management Code (ICMC) has deemed 50 mg/L of WAD cyanide released into TSFs to be safe for wildlife protection. However, this concentration is based on observations of an apparent lack of toxicity rather than a toxicological approach. The National Industrial Chemicals Notification and Assessment Scheme (NICNAS) identified in 2010 that there is a lack of toxicity data to properly assess the environmental significance of cyanide levels at gold mines. Lack of knowledge for the toxicity of free cyanide and metal cyanide complexes to wildlife led to consider alternative direct assessment techniques for designating safe levels. Whilst toxicity may be assessed by using young chickens with animal ethics approval, the traditional bioassay approach to assess cyanide toxicity is impractical for gold mine TSFs. Bioassays using algal species such as Euglena gracilis, a unicellular alga, are widely used for ecotoxicological studies. A unique feature is that the Euglena gracilis Z cell has plant-like while SMZ cell has animal-like characteristics. The aims of this project are to evaluate the suitability of Euglena gracilis Z and SMZ strains to assess the toxicity of free cyanide and both strong (cobalt) and weak (zinc, copper and nickel) acid dissociable metal-cyanide complexes that may be present in TSFs.CITATION:Noller, B N, Ng, J C, Shini, S, Breuer, P L, Sichani-Teimouri, H and Alsaadi, R N, 2014. Development of a toxicity approach to evaluate free cyanide and metal cyanide complexes in waters associated with gold and other mining, in Proceedings Life-of-Mine 2014 , pp 573–590 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 16, 2014

By Bijan Taheri, Behrouz Maghsodi, Monireh Heshami, Reza Kohan

A common problem recently encountered with the increase in the rate of input feed at Enrichment Plant 2 of the Sarcheshmeh Copper Complex is the loss of value to the tails, translating to lower recoveries. The feasibility of the direct transfer of part of the high-grade concentrate from rougher stages to an appropriate position along the circuit was studied, and two positions were proposed for direct transfer of the concentrate. One position was the feed flow into cleaner cells, and the other was the feed flow into the recleaner cell. The results indicated that transferring the concentrate from the first unit of the rougher stage to the feed flow into the cleaner cells was feasible, with no limitations, while the second position required the installation of a set of hydrocyclones. It was found that the transfer of concentrate to the proposed positions not only addressed the problem of limited cell capacity, resulting in debottlenecking of the circuit, but also improved metallurgical separation efficiency up to 1.4%.

By F. Hassani, E. Aflaki, M. Nokken, M. Kermani

"This paper presents and compares the physical properties of Gelfill and cemented hydraulic fill (CHF) obtained by lab experiments. Gelfill consists of tailings, different binders such as Portland cement, fly ash and blast furnace slag and an alkali activator such as sodium silicate. The CHF and Gelfill samples with various mixture designs were cast and cured for 28 days. The influence of sodium silicate concentration, pulp density and mixing time on the mechanical properties of samples were evaluated using the uniaxial strength test. Mercury intrusion porosimetery (MIP) was used to analyse the microstructure of CHF and Gelfill samples.This study concludes that: (i) The mechanical properties of CHF can be improved by the addition of appropriate amount of sodium silicate. (ii) The rate of strength acquisition in Gelfill samples is faster than CHF samples over 28 days of curing period. (iii) Mixing time strongly influences the mechanical properties of Gelfill samples but did not have any effect on CHF samples. (iv) The MIP analyses indicate that the pore size distribution and total porosity of Gelfill and CHF were different, and this did contribute to higher strength development of the Gelfill samples. INTRODUCTIONThe increased depths of mines in the Canadian Shield and the high stress associated with these depths favour a new method of mine backfill that can both meet strength requirements and help mine productivity. The mine backfill mainly consists of tailings, water and binder materials, the latter being most expensive. Gelfill is a new mine backfill material whose binder usually consists of alkali activators such as sodium silicate and other cementitious materials such as blast furnace slag and normal Portland cement. Although sodium silicate has been used in concrete manufacture, the use of this material in mine backfill is relatively new (Doucet, 2007, Razavi, 2007). Until very recently there have been only a few isolated publications, mostly out of McGill University, regarding mine Gelfill (Razavi, 2007 and Kermani et al., 2009 and 2010). These papers have investigated some of the basic mechanical properties and mechanical behaviour of Gelfill. However, the physical performance of Gelfill in various conditions has yet to be understood. Therefore, the main objective of this study was to investigate the influence of mixing time and sodium silicate concentration on the mechanical performance of Gelfill and CHF through a series of experiments. Moreover, the microstructure of the Gelfill and CHF samples was studied."

Jan 1, 2015

By M. Kermani

This paper presents and compares the physical properties of Gelfill and cemented hydraulic fill (CHF) obtained by lab experiments. Gelfill has an alkali activator such as sodium silicate in its materials in addition to primary materials of cemented mine backfill which are deslimed tailings, water and binders. The CHF and Gelfill samples with various mixture designs were cast and cured for 28 days. Initially, the influence of sodium silicate concentration on the mechanical properties of samples was evaluated using the unconfined compressive strength (UCS) test. Consequently, the effect of curing temperature on CHF and Gelfill samples cured in various curing temperatures ranging from 5?50 °C was studied using the UCS test. Microstructure of selected samples was studied wirth the mercury intrusion porosimetry (MIP) technique. This study concludes that: (i) The mechanical properties of CHF can be improved by the addition of appropriate amount of sodium silicate. (ii) The rate of strength acquisition in Gelfill samples is faster than CHF samples over 28 days of curing period. (iii) Curing temperature strongly influences the mechanical and microstructural properties of CHF and Gelfill samples. (iv) The microstructure analysis revealed that the addition of sodium silicate can modify the pore size distribution and total porosity of Gelfill which can contribute to the better mechanical properties of Gelfill. (v) The MIP tests suggested the microstructure of specimens were changed by adding sodium silicate in a way that the Gelfill samples had a higher percentage of fine pores than CHF samples.

Aug 1, 2013