Avirut Chinkulkijniwat

Soil Stabilization by Calcium Carbide Residue and Fly Ash

Calcium carbide residue (CCR) and fly ash (FA) are both waste products from acetylene gas factories and power plants, respectively. The mixture of CCR and FA produces a cementitious material because CCR contains a lot of Ca(OH)2, while FA is a pozzolanic material. This paper investigates the possibility of using this cementitious material (a mixture of CCR and FA) to improve the strength of problematic silty clay in northeast Thailand. The influential factors involved in this study are water content, binder content, CCR∶FA ratio, and curing time. The mechanism controlling the development of strength is also illustrated. Strength development is investigated using the unconfined compression test. A microstructural study using a scanning electron microscope and thermal gravity analysis is performed to understand the microstructural changes that accompany the influential factors. Both strength and microstructural investigations reveal that the input of CCR reduces specific gravity and soil plasticity; thus, t...

Strength development in blended cement admixed saline clay

Abstract Cement stabilization is extensively used to improve engineering properties of soft saline clays. The effect of salinity, which is modified by geological and climate changes, on the strength development in cement admixed saline clay is investigated in this paper. For a particular curing time and salt content, the strength development in saline clay admixed with cement is governed by the clay-water/cement ratio, w c / C . The strength increases with the decrease of w c / C . The increase in salt content for a particular water content decreases the inter-particle attraction of the clay and the cementation bond strength. Hence, for the same clay-water/cement ratio, the strength of the cement admixed saline clay decreases with increasing salt content. In order to increase strength, and improve the economic and environmental impact, fly ash (FA) and biomass ash (BA) can be used to substitute Portland cement. The influence of FA and BA on the strength development of cement admixed saline clay was investigated with unconfined compressive (UC) test and thermogravimetric (TG) analysis. FA and BA were dispersing materials, increasing the reactive surface of the cement grains, and hence strength increases as well. The clay-water/cement ratio hypothesis was used successfully to analyze and assess the strength development of blended cement admixed saline clay at various salt contents. An addition of 25% ash can replace up to 15.8% of cement.

Influence of Wet-Dry Cycles on Compressive Strength of Calcium Carbide Residue-Fly Ash Stabilized Clay

This article studies the durability of the calcium carbide residue (CCR) and fly ash (FA) stabilized silty clay against wetting and drying cycles to ascertain its performance in pavement applications. The durability test on the CCR-FA stabilized clay samples compacted on dry and wet sides of optimum was performed according to the ASTM. The mixture of CCR and FA can be used for soil stabilization instead of ordinary portland cement. The suitable ingredient of CCR, FA, and clay results in a moderately high strength and durability geomaterial. The durability against wetting and drying (w-d) cycles of the CCR stabilized clay is considered low according to the recommendations of the American Concrete Institute and the U.S. Army Corps of Engineers and is not accepted as a pavement material. The input FA at optimal content reacts with the excess CaðOHÞ2 from the CCR, and hence a significant improvement of the strength and durability. The optimal FA content is found at about 20%. The strength analysis shows that the durability is directly related to the unsoaked strength (prior to the w-d cycles). Consequently, a relationship between thew-d cycle strength and unsoaked strength is proposed. It is useful for quick determination of unsoaked strength during mix design to attain the target strength at the design service life. DOI: 10.1061/(ASCE)MT.1943-5533.0000853.

Stabilisation of marginal lateritic soil using high calcium fly ash-based geopolymer

Marginal soils are traditional stabilised with Portland Cement (PC) when used as a pavement material. The production of PC is however an energy-intensive process and emits a large amount of greenhouse gas into the atmosphere. Geopolymer is an environmentally friendly ‘green’ binder commonly used in building applications but rarely used in pavement applications. The application of geopolymer to marginal soil stabilisation is an innovative approach given the increasing scarcity of virgin quarry materials in many countries. This research investigates the effects of alkali activator and curing time on unconfined compressive strength (UCS) and microstructural characteristics of marginal lateritic soil (LS) stabilised with high calcium fly ash (FA)-based geopolymer, which is novel in the field of pavement geotechnics. The viability of using this stabilised material as a bound pavement material was also evaluated through laboratory evaluation tests. A liquid alkali activator was a mixture of sodium silicate (Na2SiO3) solution and sodium hydroxide (NaOH) solution at various Na2SiO3:NaOH ratios. The results showed that the UCS increased with the curing time and the 7-day UCS for all Na2SiO3:NaOH ratios tested meets the local national standard as pavement bound material for both light and heavy traffic roads. The maximum early strengths at 7 days of curing were found at Na2SiO3:NaOH of 90:10, where calcium silicate hydrate (C-S-H), cementitious products from high calcium FA and Na2SiO3, was found to play a significant role. The sodium alumino silicate hydrate (N-A-S-H) products, being time-dependent, however came into play after a longer duration. The maximum 90-day UCS was found at a Na2SiO3:NaOH ratio of 50:50. This study indicated that marginal LS could be stabilised by high calcium FA-based geopolymer and used as an environmentally friendly pavement material, which would furthermore decrease the need for high-carbon PC. The economical Na2SiO3:NaOH ratio for both light and heavy traffic pavement materials was suggested to be 50:50.

Field strength development of repaired pavement using the recycling technique

The pavement recycling technique is a way to effectively repair damaged pavements. In this study, statistical analysis shows that the field strength is significantly lower than the laboratory strength. The mixing process used in the pavement recycling technique does not significantly affect the field strength reduction, as indicated by the small variation of the field hand-compacted strength (qufh) and the laboratory strength (qu1). The curing conditions do significantly control the field strength development. A factor of safety of 2.0 is recommended for design. The strength development mainly depends on the soil-water/cement ratio (w/C) and curing time regardless of the level of compaction energy. A general strength development model as a function of w/C and curing time is introduced. Only two laboratory strength data from the specimens cured at two different curing times are required in the proposed model. A high accuracy of the strength prediction is reported. This proposed model is a very powerful tool that determines the strength development of cement-stabilized coarse-grained soil after 7 days of curing. It can also be used to determine the correct quantity of cement to be stabilized for different field mixing water contents, compaction energies and curing times.

Water-Void to Cement Ratio Identity of Lightweight Cellular-Cemented Material

AbstractLightweight cellular cemented clays have wide range of applications in the infrastructure rehabilitation and in the construction of new facilities. Since the inception of this method, the developments in the plant and machinery as well as associated field techniques have surpassed the basic understanding of strength developments in lightweight cellular cemented clay. In this paper, an attempt is made to identify the dominant parameter, governing the unit weight, strength, and compressibility characteristics of lightweight cellular cemented clay, which helps control input of water, air foam, and cementing agent to attain unit weight and strength development with curing time. From this research, it is discovered that water-void/cement ratio, wV/C is the dominant parameter for the above purposes. From the critical analysis of test results, a mix design method to attain the target strength and unit weight is suggested. This method is useful from both engineering and economic perspectives.

Effect of fly ash on properties of crushed brick and reclaimed asphalt in pavement base/subbase applications

Fly Ash (FA), an abundant by-product with no carbon footprint, is a potential stabilizer for enhancing the physical and geotechnical properties of pavement aggregates. In this research, FA was used in different ratios to stabilize crushed brick (CB) and reclaimed asphalt pavement (RAP) for pavement base/subbase applications. The FA stabilization of CB and RAP was targeted to improve the strength and durability of these recycled materials for pavement base/subbase applications. The Unconfined Compressive Strength (UCS) and resilient modulus (MR) development of the stabilized CB and RAP aggregates was studied under room temperature and at an elevated temperatures of 40°C, and results compared with unbound CB and RAP. Analysis of atomic silica content showed that when the amount of silica and alumina crystalline was increased, the soil structure matrix deteriorated, resulting in strength reduction. The results of UCS and MR testing of FA stabilized CB and RAP aggregates indicated that FA was a viable binder for the stabilization of recycled CB and RAP. CB and RAP stabilized with 15% FA showed the highest UCS results at both room temperature and at 40°C. Higher temperature curing was also found to result in higher strengths.

Recycled asphalt pavement – fly ash geopolymers as a sustainable pavement base material: Strength and toxic leaching investigations

In this research, a low-carbon stabilization method was studied using Recycled Asphalt Pavement (RAP) and Fly Ash (FA) geopolymers as a sustainable pavement material. The liquid alkaline activator (L) is a mixture of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH), and high calcium FA is used as a precursor to synthesize the FA-RAP geopolymers. Unconfined Compressive Strength (UCS) of RAP-FA blend and RAP-FA geopolymer are investigated and compared with the requirement of the national road authorities of Thailand. The leachability of the heavy metals is measured by Toxicity Characteristic Leaching Procedure (TCLP) and compared with international standards. The Scanning Electron Microscopy (SEM) analysis of RAP-FA blend indicates the Calcium Aluminate (Silicate) Hydrate (C-A-S-H) formation, which is due to a reaction between the high calcium in RAP and high silica and alumina in FA. The low geopolymerization products (N-A-S-H) of RAP-FA geopolymer at NaOH/Na2SiO3=100:0 are detected at the early 7days of curing, hence its UCS is lower than that of RAP-FA blend. The 28-day UCS of RAP-FA geopolymers at various NaOH/Na2SiO3 ratios are significantly higher than that of the RAP-FA blend, which can be attributed to the development of geopolymerization reactions. With the input of Na2SiO3, the highly soluble silica from Na2SiO3 reacted with leached silica and alumina from FA and RAP and with free calcium from FA and RAP; hence the coexistence of N-A-S-H gel and C-A-S-H products. Therefore, the 7-day UCS values of RAP-FA geopolymers increase with decreasing NaOH/Na2SiO3 ratio. TCLP results demonstrated that there is no environmental risk for both RAP-FA blends and RAP-FA geopolymers in road construction. The geopolymer binder reduces the leaching of heavy metal in RAP-FA mixture. The outcomes from this research will promote the move toward increased applications of recycled materials in a sustainable manner in road construction.

Environmental impacts of utilizing waste steel slag aggregates as recycled road construction materials

Slag is an industrial waste generated during the steelmaking process. Electric arc furnace slag (EAFS) and ladle furnace slag (LFS) are both produced at different stages of steelmaking process, respectively, in electric arc furnaces and refining ladle furnaces. As part of this research, an extensive suite of engineering and environmental tests were undertaken on steel slag aggregates to evaluate their potential usage as road construction materials. The engineering assessment included particle size distribution, hydrometer, organic content, flakiness index, Atterberg limits, particle density, water absorption, pH, minimum and maximum dry densities with a vibrating table, modified compaction, California bearing ratio (CBR) and Los Angeles abrasion tests. In addition, a suite of environmental tests comprising total and leachable heavy metal tests were undertaken on both types of steel slag aggregates. From an environmental perspective, EAFS and LFS were found to pose no environmental risks for use as aggregates in roadwork applications. The engineering properties of LFS aggregates with its satisfactory geotechnical and environmental results, particularly its high CBR values, indicated that the material was ideal for usage as a construction material in roadwork applications such as pavement base/subbases and engineering fills. EAFS, with its comparatively lower CBR value, was found to be only suitable to use as a construction material for pavement subbases and engineering fills. The usage of steel slag aggregates in roadwork applications would bring about a practical end-of-life alternative for their sustainable reuse and possibly divert large amount of these waste materials from landfills.

Modeling of Coupled Mechanical–Hydrological Processes in Compressed-Air-Assisted Tunneling in Unconsolidated Sediments

This paper presents an analysis of coupled hydrological–mechanical processes in the construction of tunnels using the compressed air technique. The compressed air is applied in the tunnel space during the construction to prevent a water inflow. The paper uses a methodology that links two computer codes TOUGH2 and FLAC3D such that hydrological-mechanical analysis can be conducted. An air flow test conducted in Essen, Germany, was simulated, and the results agreed well with the field measurements. Subsequently, a numerical simulation of compressed air tunneling was performed to analyze the air injection rate and the surface displacements. The calculated air losses from the tunnel are within the range of the field observations. The analysis of surface settlement shows upward heaving and a decrease in the magnitude of surface settlement, which is consistent with the field observations.