Increasing Replacement Ratio Research Articles

Thermoelectric behaviors of fly ash and metakaolin based geopolymer

In this paper, the thermoelectric behaviors of fly ash and metakaolin based geopolymer were investigated. It was found that the seebeck coefficient of geopolymer paste is much higher than that of cement paste, indicating geopolymer may be a promising thermoelectrical material. The influences of different parameters were discussed. The seebeck coefficient for both fly ash and metakaolin based geopolymers were found to increase with the increase of alkali concentration. The curing temperature has a more significant influence on the thermoelectric behavior of fly ash based geopolymers. Meanwhile, the increase of slag replacement ratio would result in a decreased seebeck coefficient for fly ash based geopolymer.

Stability analysis of vertical caisson breakwater on soft intercalated ground under cyclic loading

A vertical caisson breakwater on soft intercalated ground (sand replacement in the upper layer) is highly susceptible to catastrophic failure when subjected to excessive cyclic loadings. In this paper, the cyclic stability of a caisson-rubble-ground system under different sand replacement conditions is investigated via finite element methods. Structure-soil interfaces and undrained strength degradation of the soft intercalated layer are two key considerations. The latter is implemented by modifying the Yasuhara model to quantify the strength degradation in terms of the number of cycles and stress level. Cyclic responses with different replacement ratios r (i.e., the ratio of backfilled sand layer thickness to initial total soft layer thickness) are presented in terms of pore pressure and strength degradation. Failure modes and safety factors are also investigated. Numerical results show that the pore pressure and strength degradation of the soft layer mainly occurred underneath the rubble mound, and were evident at small replacement ratios. The failure modes could be caisson sliding (r ≤ 0.35), soft ground bearing capacity failure (r > 0.50), or a combination thereof (0.35<r ≤ 0.50). The safety factor first increased and then approached a constant value with increasing replacement ratios. The findings herein provide a practical implication for safety evaluation and structural design.

Effect of fly ash and superabsorbent polymer on concrete self-healing ability

Concrete that contains self-healing supplementary materials is a feature of many sustainable structures because it decreases maintenance costs and extends service life. Many self-healing studies have suggested that concrete needs to have extensive exposure to water in order to promote crack-sealing. This paper investigates the benefits of using fly ash and superabsorbent polymer (SAP) to promote self-healing. Eight mix proportions with varying fly ash and SAP replacement ratios were examined. Self-healing efficiency was evaluated by temporal decreases in water discharge through a crack, crack closure observation, stereomicroscopy, scanning electron microscopy (SEM), thermogravimetric/differential thermal analysis (TG/DTA), and energy-dispersive X-ray spectroscopy (EDS). The specimens were preloaded to generate a crack, and these pre-cracked specimens were healed either by continuous water immersion or exposure to wet-dry conditions. Crack width was found to decrease with increase in the fly ash replacement ratio, whereas higher volume of SAP was found to mitigate water discharge through the crack by the swelling of the SAP gel. These effects in combination achieved a maximum of 100% crack closure and permeability restoration by 28 days of healing. As the results, midterm self-healing ability of concrete can be enhanced by the coupling effect of fly ash and SAP. The crack closure was found to be associated with the development of self-healing products such as calcium carbonate and C-S-H.

High temperature influence on concrete produced by spherical shaped EAF slag fine aggregate – Physical and mechanical properties

Spherical shaped EAF slag fine aggregate is a promising alternative of natural sand in concrete as it imparts improved mechanical, durability and thermal properties. These features indicate the possibility of obtaining concrete of improved fire resistance by using spherical shaped EAF slag fine aggregate which have not yet been studied. The basic intent of this study is to investigate the high temperature response of concrete produced by spherical shaped EAF oxidizing slag fine aggregates. In this study, seven different types of concrete were produced by replacing natural sand with spherical and angular shaped EAF slag fine aggregates at a volume ratio of 0.0, 0.3, 0.5 and 1.0 for the water to cement ratio (W/C), slump and air content of 0.4, 5 cm and 5% respectively. The specimens were heated in the electric furnace at four different temperature state ranging from 200 °C to 1000 °C after a curing age of 28 days. All the specimens (both heated and sound) were tested for physical properties such as mass loss, length change and mechanical properties such as compressive strength, elastic modulus, flexural strength and tensile fracture energy. Results indicate that spherical shaped EAF slag concrete being exposed to high temperature undergoes lower mass loss with the increase in slag replacement ratio and the values are lower than angular shaped EAF slag concrete of same slag ratio. In addition, up to a heating temperature of 500 °C, spherical shaped EAF slag concrete exhibits superior residual elastic modulus and similar to slightly decreasing residual compressive and flexural strength in comparison to normal concrete.

Effects of crushed stone waste as fine aggregate on mortar and concrete properties

In this study, effects of crushed stone waste from Katunun’s quarry as fine aggregate on mortar and concrete properties will be examined. Samples with varying crushed stone waste replacement ratio, ranging between 0% until 100%, will be analysed at 3, 7 and 28 days curing time. Mortar sample is using 0.5 w/c ratio, while concrete sample is using 0.45 w/c ratio. The mixture of mortar sample is based on SNI 03-6825-2002, whilst concrete sample is based on SNI 03-2834-2000. The examination of concrete samples workability was conducted based on the slump test according to SNI 1972:2008. Moreover, the compressive strength test of mortar sample is based on SNI 03-6825-2002. In addition, the compressive strength test of concrete sample is based on SNI 1974:2011. Regarding compressive strength of mortar samples, the average compressive strength results of mortar with crushed stone waste rose significantly in line with the increase in replacement ratio. As for the workability of fresh concrete, sample using natural river sand had better workability compared to sample using crushed stone waste. However, the workability of concrete with crushed stone waste is still meet the slump value specified in the job mix formula. In addition, it has been found out that the combination of 75% crushed stone waste with 25% river sand will give the highest compressive strength compared to others combinations. Based on these findings, the utilization of crushed stone waste from Katunun’s quarry in mortar and concrete mixture can be proposed.

Chloride resistance and binding capacity of cementitious materials containing high volumes of fly ash and slag

A systematic study on the chloride penetration resistance and binding capacity of cementitious materials containing varying proportions of low-calcium fly ash or blast-furnace slag is presented. The results show that a larger water/binder ratio of cementitious materials can enhance its binding capacity but reduce chloride resistance regardless of binder type. At a given water/binder ratio, the chloride-binding capacity of cementitious binder plays an important role in its chloride resistance in the saturated condition. Fly ash can improve the chloride resistance and binding capacity of cementitious binders with the gradual increase of fly ash replacement ratio up to 70%. However, slag-blended cementitious binder shows the highest chloride resistance and binding capacity when the slag replacement ratio is about 40%. A higher volume of slag can result in a decline of chloride resistance and binding capacity. In addition, the Freundlich isotherm provides the best fit for describing the chloride-binding capacity of cementitious materials, regardless of water/binder ratio and binder type.

Incorporation of bamboo charcoal for cement-based humidity adsorption material

Abstract This paper investigates the incorporation of bamboo charcoal (BC) in cement to prepare cement-based humidity adsorption material. Cement pastes with BC were prepared and their flowability, compressive strength, drying shrinkage and humidity adsorption were measured. Pore information of hardened paste was determined by both N2 adsorption (NAD) and mercury intrusion porosimetry (MIP) analyses. Results indicate that BC decreases flowability of cement paste but favorable flowability of blended paste with BC can be provided by adjusting superplasticizer dosage. BC decreases compressive strength of hardened cement paste before 7 d while its influence on later strength depends on its particle size and replacement ratio. Specifically, BC with average size of 8 μm increases compressive strength at later ages at 10% replacement ratio. But this improvement is diminishing with the increase of either BC size or replacement ratio and adverse effects on compressive strength are found for mixtures with BC of larger size, especially at higher replacement ratios. BC of 23 μm shows little influence on drying shrinkage of mixtures while that of 8 μm significantly increases this value as replacement ratio rises. The humidity adsorption results demonstrate that BC increases the humidity adsorption capacity of cement paste and this improvement is more prominent when BC ratio is higher or BC is finer. The calculated humidity adsorption results show a favorable agreement with experimental ones with the deviation probably attributed to experiment technique limits. It is inferred that humidity adsorption promotion is mainly due to the combined effects of BC on pore volume and specific surface area of hardened paste.

Numerical study of dynamic stress developed in the high speed rail foundation under train loads

As a ground treatment method, geosynthetic-reinforced pile foundation (GRPF) is widely applied in the railway construction, especially in high-speed railway (HSR), due to the strict restrictions on post-construction settlement. The post-construction settlement is commonly considered induced by the weight of railway structure as well as the moving train load. Therefore, the dynamic stress developed in the GRPF induced by HSR is important for the post-construction settlement study. However, most studies focus on the dynamic stress on the track and subgrade, studies concerning dynamic stress in GRPF are few. In this paper, a three-dimensional time-domain viscoelastic finite element method (FEM) model is developed to study the dynamic response of GRPF under the high-speed rail load. The simulation model is verified by a comparison with the results of analytical solution. And based on this model, parameter study is conducted. The investigation of train speed and the pile group layout has shown that the dynamic stress amplitude significantly increases after the train speed reaches the Rayleigh wave velocity of the subgrade, while the pile-soil stress acts reversely. For the influence of the pile group layout, three variables: pile cap size, longitudinal pile spacing, and lateral pile spacing are studied respectively. A parametric study of pile cap size, longitudinal pile spacing and lateral pile spacing have suggested that the amplitude of dynamic stress developed in the soil is more susceptible to the pile spacing rather than pile cap size. Besides, increasing replacement ratio results in the decrease of dynamic pile-soil stress ratio.

Fresh and Mechanical Properties of Self-Compacting Rubber Lightweight Aggregate Concrete and Corresponding Mortar

Increasing amount of waste tires caused huge environment issues in recent years. Recycling concrete is an effective way. In this paper, waste tires are crushed into particles and incorporated in lightweight aggregate concrete to prepare a special concrete (self-compacting rubber lightweight aggregate concrete (SCRLC)). A detailed experimental research of effects of rubber particles on the properties of SCRLC and corresponding mortar is conducted. The results show that increasing the rubber particles replacement ratio leads to a raising of yield stress and plastic viscosity of mortar pastes. Flowability, filling capacity, and passing ability of SCRLC decline and the segregation resistance property of SCRLC improves as the rubber particles replacement ratio increases. Well, linear correlations between slump flow of SCRLC and shear stress of corresponding mortar pastes and segregation ratio of SCRLC and plastic viscosity of corresponding mortar pastes are obtained. In order to ensure that rubber lightweight aggregate concrete can compact by itself, the upper limit of shear stress of corresponding mortar pastes is 231.7 Pa and the lower limit of plastic viscosity of corresponding mortar pastes is 3.72 Pa·s. Compressive strength, splitting tensile strength, flexural strength, and elastic modulus of SCRLC and compressive strength of corresponding mortar decrease as the rubber particles replacement ratio increases. The 28-day compressive strength of SCRLC can meet the requirements of lightweight aggregate concrete structures until the rubber particles replacement ratio reaches 50%.

Mechanical properties of seawater sea-sand concrete reinforced with discrete BFRP-Needles

To recycle the fiber-reinforced polymer (FRP) waste, a new type of discrete slender FRP element reinforced seawater sea-sand concrete (SWSSC) was proposed in this paper. This element, referred to as “Basalt-FRP (BFRP)-Needles”, is produced by cutting BFRP bar waste into 100 mm rod-shaped elements. BFRP-Needles were incorporated into SWSSC to partially replace the coarse natural aggregate by volume. Test results indicate that there was no significant difference in the compressive strength for SWSSCs that incorporated 6 mm, 8 mm or 10 mm BFRP-Needles with the same volume replacement ratio. When the volume replacement ratio was less than 15%, the compressive strength decreased with the increasing replacement ratio, and the maximum decrease was 10%. The splitting tensile strength of specimens with a 5%, 10%, 15%, and 20% volume replacement ratio was increased by 4%, 11%, 2%, and 32%, respectively, compared to that of the NA (Control) specimen. The flexural strength of specimens with a 5%, 10%, 15%, and 20% volume replacement ratio was decreased by 6%, 14%, 10%, and 6%, respectively, compared to that of the NA (Control) specimens. The incorporation of BFRP-Needles in SWSSC resulted in significant increases in the fracture toughness, especially for the high volume replacement ratio of 20%.

Use of Rice Husk Ash as Strength-Enhancing Additive in Lightweight Cementitious Composite Mortars

This paper investigates the properties of rice husk ash (RHA) produced by using a ferro-cement furnace. The effect of RHA percentage on lightweight composite mortar consistency, initial and final setting time, plastic and dry set density, flexural and compressive strength were investigated. Incorporation of RHA in lightweight mortar increased water demand. The effect of early (7 and 14 days) and long term curing ages (90 and 120 days) on the mechanical strength properties of lightweight composite mortars with RHA were also analysed. Mortar samples show strength reduction of 10.6% and 8.57% compared to the control mix at early curing ages of 7 and 14 days, respectively. RHA mortar gave excellent improvement in strength for 20% replacement (18.85% and 21.69% increment compared to the control mix at long term curing of 90 and 120 days), and up to 25% of cement by weight be valuably replaced with RHA without adversely affecting the strength. Increasing replacement ratio of RHA enhanced the strength of blended mortar compared to low utilization ratio of RHA and control OPC mixtures.

Carbonation Behavior of Repeated Recycled Fine Aggregate Concrete under Bending Load

Carbonation resistance is an important factor affecting the durability of concrete, and the carbonation behavior of structural concrete become more complex under loading. In order to investigate the feasibility of utilizing Recycled Fine Aggregate (RFA) in structural concrete under a coupling of bending load and carbonation, two generations of repeatedly Recycled Aggregate Concrete (RAC1 and RAC2) with four different replacements level (10%, 20%, 30%, and 40%) of Natural Fine Aggregate (NFA) by RFAs were prepared, and carbonation depths of all concrete mixes were tested under an action of bending load of 40, 70, 100, and 120% of failure load. The results indicated that the repeated RAC successfully reached the target slump and target compressive strength, despite both workability and compressive strength decreased with increasing RFA replacement ratio. The carbonation depth of repeated RAC increased with the increasing replacement ratio of RFA. With bending load increasing, the carbonation depth of repeated RAC also increased except for the specimens suffered 70% of failure load. The resultant insights demonstrate the feasibility of using repeated RAC to design a service lifetime of 50 years in practical engineering.

Effect of macro-synthetic fibers on the fracture energy and mechanical behavior of recycled aggregate concrete

In order to achieve sustainability in construction industry, recycling of construction and demolition wastes in new concrete is gaining a lot of attention. However, extensive research is needed to explore the complete behavior of resulting recycled aggregate concrete (RAC). This study aims to investigate the fracture behavior, mechanical performance and microstructure of macro-synthetic fiber reinforced RAC. For this purpose, notched beam specimens were produced using three different replacement ratios of recycled concrete aggregates (RCA) (i.e., 0, 50% and 100%) and three different dosages of macro-synthetic fibers (i.e., 0, 0.5% and 1% of volume of RAC). Three-point bending and other mechanical tests were performed to investigate the post peak behavior (residual flexural tensile strength, fracture energy and toughness) and mechanical properties (compressive strength, flexural strength and split tensile strength) of macro-synthetic fiber reinforced normal and RAC. Fracture surface analysis was also performed to develop the empirical relationships between number of fibers and post peak behavior of fiber reinforced RAC. Furthermore, microstructure characteristics of macro-synthetic fiber reinforced normal and RAC were also investigated using scanning electron microscopy (SEM). Results showed that reduction in mechanical properties of concrete was observed with the increase in RCA replacement ratio. However, increase in mechanical properties particularly split tensile strength of normal and RAC was observed with the increase in dosage of macro-synthetic fibers. Concrete specimens also showed increase in residual flexural tensile strengths with the increase in dosage of macro-synthetic fibers. RAC reinforced with 1% dosage of macro-synthetic fibers showed increase in fracture energy and toughness by 380% and 129%, respectively. A strong influence of number of fibers on residual flexural tensile strength and fracture energy of concrete mixtures was observed during the study. Microstructural analysis also showed the existence of bond between mortar paste and macro-synthetic fiber, which improved the mechanical properties and post peak behavior of macro-synthetic fiber reinforced concrete. Based on this study, it can be concluded that macro-synthetic fibers improve the fracture energy and mechanical properties of RAC leading towards higher ductility and better energy dissipation. Moreover, number of fibers strongly influences the residual flexural tensile strength and fracture energy of RAC.

Effect of fineness and replacement ratio of ground fly ash on properties of blended cement mortar

This study presents an experimental investigation on the effect of ground fly ash fineness and replacement ratio on properties of blended cement mortar. Class F fly ash was ground into three different fineness values of 4610 cm2/g, 5690 cm2/g, and 6300 cm2/g with ball grinding machine and used as a replacement ratios of 0%, 10%, 15%, and 20% by weight of cement to produce the blended cement mortars. Compressive strength test, water absorption, mercury intrusion porosimetry (MIP) test, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis were performed. Test results show that the use of fly ash resulted in significant improvement in compressive strength and substantial decrease in water absorption and capillary pores for blended cement mortars compared to OPC mortar. The mortars with fineness value of 5690 cm2/g and FA replacement ratio of 20% has the highest compressive strength and lowest water absorption and smallest porosity. The XRD analysis showed that Ca(OH)2 is one of the hydration products during the hydration reaction. When fly ashes were incorporated into the blended cement mortars, the intensity peaks of Ca(OH)2 in the XRD patterns decreased. The increasing replacement ratio of fly ash decreased Ca(OH)2. Based on the results, both the fly ash fineness and the fly ash replacement ratio have a significant influence on the properties of blended cement mortar.

Dynamic stability of composite foundation under different area replacement ratio based on intelligent sensing technology

Oil storage tanks are widely used in petrochemical industry. But the improper foundation treatment is likely to cause the damage of structure and accessory components under the action of earthquake, as a result, environmental pollution and fire will be caused by chemical leakage. Therefore, it is necessary to study the dynamic stability and the security affecting factors of composite foundation. Taking foundation treatment of one oil depot belong to Petro China as the engineering background, the discrete compacted piles arranged by equilateral triangle are simplified by the equivalent continuum method. Contacts are set between pile and soil, between concrete foundation and subsoil, and between concrete foundation and tank to reflect the mechanical behavior of the system as far as possible. The composite foundation with three kinds of area replacement ratios are studied by the dynamic stability analysis. The results show that safety factors corresponding to the three area replacement ratios are all greater than the general safety factor 2 which is required in engineering; the dynamic safety factors increase with the increase of area replacement ratio. Besides, area replacement ratio has a great influence on the distribution of plastic zone. Therefore, in the actual project, taking into account the dynamic safety factor and the distribution of plastic zone, there is an optimal area replacement ratio, and it may not only meet requirements for engineering safety, but make use of materials rationally and increase economic benefits.

Electrochemical feature for chloride ion transportation in fly ash blended cementitious materials

The chloride transport behavior of fly ash blended cement material was investigated in this study by using electrochemical impedance spectroscopy (EIS). The chloride penetration was studied by means of EIS. A new equivalent circuit model was applied to describe the electrochemical system of fly ash blended cementitious materials. Experimental results demonstrate that the increase in the fly ash replacement ratio of sample can increase the penetration depth of chloride ion. In addition, the increase in the fly ash replacement ratio of sample can enlarge the Nyquist curve semi-circle, and improve ion transfer resistance at the solid-liquid phase interface. We determined the quantitative relationship between electrochemical properties and chloride penetration depth in order to successfully predict the chloride ion penetration depth of blended cements with varying fly ash content. It is expected to complement the existing test standards regarding the durability evaluation of construction materials.

Consolidation of composite ground improved by granular columns with medium and high replacement ratio

As pointed out in the Technical Standards and Commentaries for Port and Harbour Facilities in Japan (2009), the consolidation rate of subsoil improved by the sand compaction pile with high replacement ratio tends to be delayed compared to that predicted by Barron’s equation (1948). Moreover, the time delay in consolidation becomes greater with an increase in the replacement ratio. This finding cannot be interpreted by the conventional theories. In this context, this paper attempts to interpret this finding by employing two analytical models previously developed by the authors, and by taking the consolidation of column itself into consideration. Moreover, these two analytical models are further extended to predict the consolidation rate under multiple instantaneous loading and multiple ramp loading. Then they are compared to a conventional model with no consideration of column itself. The results show that the conventional model, which does not consider column consolidation, will overestimate the average degree of consolidation, and that the overestimated value increases exponentially with the increase in the replacement ratio. Especially in the case of medium and high replacement ratios, the maximum overestimated average degree of consolidation may increase from 12% to 43% when the replacement ratio increases from 0.4 to 0.8. The time delay observed when using these two analytical models in predicting the consolidation rate is in good agreement with the finding revealed in the Technical Standards and Commentaries for Port and Harbour Facilities in Japan (2009). In particular, a simple relation is derived to calculate the time delay in a simple and explicit way. Finally, the present models are applied to a case study to verify their feasibility in predicting settlement during consolidation.

Performance of Granular Piles-Improved Soft Ground Under Raft Foundation: A Numerical Study

Reinforcing soft soil with granular piles improves effectively its properties. In the current research, the performance of granular piles reinforced soft soil under a uniformly loaded raft foundation has been investigated numerically utilizing Plaxis 3D. A parametric study was performed under drained loading conditions to investigate the effect of various parameters on the long-term behavior of the raft foundation such as spacing distance, diameter and length of the granular piles. The influence of the parameters has been studied on the overall settlement, bending moment of the raft and the lateral bulging of the granular piles. The results indicated that the existence of the granular piles in soft soil decreases significantly the settlement and the bending moment of the raft. The lateral bulging distribution of the granular piles is dependent on their locations. Additional improvements in the settlement and the bending moment of the raft, and in the lateral bulging also occurred due to the decrease of the spacing ratio, and the increase of area replacement ratio and granular piles length. Reinforcing soft soil using floating ground piles with length to soil layer thickness ratio of 0.75 is sufficient to achieve good improvement performance.

Silicon carbide waste as a source of mixture materials for cement mortar

This paper presents an investigation of the feasibility of recycling silicon carbide waste (SCW) as a source of mixture materials in the production of cement mortar. Mortars with SCW were prepared by replacing different amounts of cement with SCW, and the properties of the resulting mortars, such as the fluidity, strength and shrinkage, were studied in this work. Thermogravimetry-differential scanning calorimetry and scanning electron microscopy were employed to understand the reasons for the property changes of the mortars. The results indicate that SCW decreases the initial and 1-h fluidity of fresh mortar but improves the loss of fluidity. The mortar with SCWexhibits a lower strength at 3 d and 7 d but a higher strength at 28 d and 56 d compared to the control. The shrinkage rate of cement mortar with SCW shows an obvious decrease as the replacement ratio increases. In addition, the content of calcium hydroxide in hardened paste also shows that SCW has some impact on the hydration of the cement-SCW system. The microstructures of the hardened paste also show evidence for a later strength change of mortar containing SCW. This work provides a strategic reference for possibly applying SCW as a mixture material in the production of cement mortar.

Compressive behavior of steel fiber reinforced recycled coarse aggregate concrete designed with equivalent cubic compressive strength

This paper presents the experimental results related with the compressive behavior of steel fiber reinforced-recycled coarse aggregate concrete (SFRCAC). Compressive strength, Young’s modulus and stress-strain curves were carried out on more than 100 specimens. Emphasis was placed on the combined effect of steel fibers (SFs) and recycled coarse aggregate (RCA) on the axial compressive behavior of SFRCAC with equivalent compressive strength. Test results indicate that with the addition of SFs, Young’s modulus and stress-strain curves of SFRCAC are similar to those with natural coarse aggregate (NCA) concrete, but the critical strain has a significant increase with the increase of steel fiber content and RCA replacement ratio. Regression formula of compressive strength, Young’s modulus, critical strain and constitutive model of SFRCAC are proposed.