Abstract

Recycling of abandoned waste bottom ash has been a key issue in Republic of Korea in terms of environmental protection as well as economic concern. In this work, a method for recycling of abandoned bottom ash has been discussed based on the results from laboratory and industrial-scale experiments. Abandoned bottom ash was magnetically separated and properties of magnetically separated bottom ash samples as well as properties of mortar and masonry cement brick made of bottom ash were investigated. According to the experimental results, bulk and skeletal densities were ranked in the order of strongly magnetic > weakly magnetic > as-received > non-magnetic (from heavier to lighter) bottom ash. From laboratory-scale experiments, compressive strengths of mortars made of bottom ash samples (measured by ASTM C 109) were lower than that of mortar made of standard sand. Among bottom ash samples, mortar made of non-magnetic bottom ash (after removal of unburnt carbon) showed higher compressive strength with lower thermal conductivity (measured by ASTM C 1113) and weight than others. Masonry cement brick made of magnetic bottom ash showed lower weight and thermal conductivity than those made of standard sand, while meeting the KS strength guideline as a masonry cement brick. The results suggest the applicability of bottom ash as lightweight aggregate for production of masonry cement brick. However, considering the lower strength obtained from masonry cement brick made of as-received bottom ash (without removal of unburnt carbon), unburnt carbon content should be removed prior to its utilization as lightweight aggregate.

Introduction

Consumption of fossil fuels for operation of coal fired power plant has been consistently increasing all over the world (International Energy Agency, 2009; Korre et al., 2010; Leblond, 2006; Shafiee & Topal, 2008). Although reduction in CO2 emission is very critical issue in this industry (Hussain et al., 2022), recycling of waste by-products is as important issue as the reduction of CO2 emission in terms of environmental protection (Abbas et al., 2020; Bui et al., 2019; Lee et al., 2020; Meek et al., 2021; Oakes et al., 2019) considering the amount of waste that has been generated so far. Approximately 730 million tons of bottom ash (Abbas et al., 2020) and 600 million tons of fly ash (Çiçek & Çinçin, 2015; Nyale et al., 2013) are annually produced in the world. Although fly ash has been successfully utilized as a supplementary cementitious material due to its beneficial properties such as reduction in the heat of hydration (Atiş, 2002a, 2002b; Langan et al., 2002; Matos et al., 2020; Nocuń-Wczelik, 2001; Schindler & Folliard, 2005), improvement in workability (Atiş, 2002b; Leung et al., 2016; Nocuń-Wczelik, 2001; Uysal et al., 2012; Yao et al., 2015), and long-term strength and durability (Pala et al., 2007; Siddique, 2003; Tikalsky et al., 1988), most of the bottom ash has not been recycled and abandoned in the waste storage site.

The utilization of bottom ash as a supplementary cementitious material has been limited. The chemical compositions of bottom ash are similar to that of fly ash. However, the particle size is larger and the structure is more crystalline than fly ash. For this reason, the pozzolanic activity of bottom ash is very weak. The work of (Cheriaf et al., 1999) showed that bottom ash did not react with calcium hydroxide at early ages. The pozzolanic activity was very slow until 28 days, and became accelerated after 90 days. Jurič et al. (Jurič et al., 2006) recommended to replace up to 15 wt% of cement by bottom ash to use it as a supplementary cementitious material. Kula et al. (Kula et al., 2002) showed that bottom ash can be used as a supplementary cementitious material depending on its particle size distribution. Jaturapitakkul et al. (Jaturapitakkul & Cheerarot, 2003) observed a glassy aluminosilicate phase (diffused halo maxima) at 20–27° 2θ (Cheriaf et al., 1999; Chindaprasirt et al., 2009) that can be a source of pozzolanic reaction, but reported that the pozzolanic activity of bottom ash can be increased by grinding the particle size lower than 45 μm. According to the literature, pozzolanic activity of bottom ash was so slow or weak that it cannot be effectively utilized as a supplementary cementitious material without additional mechanical or chemical treatment (Filipponi et al., 2003; Liu et al., 2018; Mangi et al., 2018).

Conclusion

In this work, magnetic separation was applied on bottom ash that was stored in the pond site of Hadong coal fired power plant. Properties of magnetically separated bottom ash were analyzed, mortar specimens as well as masonry cement brick samples were prepared, and compressive strength, water absorption, and thermal conductivity were measured. According to the results obtained from this work, following conclusions can be drawn.

1) Magnetic separation with 1000 and 3000 gauss magnet was effective for separating bottom ash samples that contains higher amount of magnetite. As a result, bulk and skeletal density of strongly magnetic bottom ash were higher than those of as-received bottom ash. Non-magnetic bottom ash showed the lowest bulk and skeletal density.

2) Pozzolanic activity of bottom ash was ranged 53 ~ 62% of fly ash that was stored at the same pond site. Considering the particle agglomeration observed from the fly ash, it is possible to evaluate the pozzolanic activity of bottom ash either as non-pozzolanic or as very weakly pozzolanic.

3) From laboratory scale experiments, non-magnetic bottom ash showed the better performance than strongly magnetic bottom ash in terms of compressive strength and thermal conductivity. Since large amount of unburnt carbon stayed together with non-magnetic bottom ash, removal of unburnt carbon is a key factor for successful utilization of non-magnetic bottom ash.

4) Masonry cement brick made of magnetic bottom ash showed 40% reduction in unit weight, 20% reduction in thermal conductivity. Utilization of non-magnetic bottom ash for masonry cement brick production after removal of unburnt carbon can also be a successful application, considering the results from laboratory-scale experiments (density and thermal conductivity was lower for non-magnetic bottom ash).

Abstract

This study evaluated the potential of sugarcane bagasse fly ash, collected from boiler exhaust stacks via a bypass pipe, as a renewable supplementary cementitious material. The bagasse fly ash was ground into three different particle sizes (D50 of 10, 20, and 30 μm) and characterized in terms of morphology, porosity, specific surface area, and pozzolanic activity. The influence of the ashes on paste hydration was investigated using isothermal calorimetry. Mortars were then tested with 20% cement replacement by fly ash, analyzing packing density, compressive strength evolution, and durability against sulfuric acid. Results indicated the suitability of the fly ash as a supplementary cementitious material, with low contamination and greater pozzolanic activity at smaller particle sizes. This enhanced initial hydration and long-term strength, with finer ashes showing superior mechanical properties when compared to the reference mortar (an 8% increase). Mortars with fly ash exhibited higher packing density and reduced mass loss under sulfuric acid attack, but increased water absorption and capillarity, alongside decreased compressive strength compared to the reference. Briefly, the findings highlighted that the potential of bagasse fly ash as a promising low cost and eco-beneficial material for sustainable construction practices.

Introduction

It is imperative to act now to reduce global environmental impacts by combating CO2 emissions and preserving our planet for future generations. The cement industry plays a pivotal role in the necessary reduction of global emissions, requiring innovation and more sustainable practices to build a greener and healthier future for our planet. On the other hand, industrial waste discharged into the soil poses a significant environmental threat and can lead to soil contamination, compromising agricultural land quality, groundwater, and overall ecosystem health ( Mohan et al., 2023 ). Sales and Lima (2010) emphasized the negative impact of improper disposal and the use of these residues as fertilizers, especially in powder form, due to their low soil enrichment potential.

In this scenario, sugarcane bagasse ash (SCBA), an abundant residue generated globally every year, is of paramount importance, particularly in the cement industry, with its silica-rich composition making it an attractive and valuable resource. Thus, SCBA is a promising pozzolanic material, recognized in several studies conducted in recent decades ( Ahmad et al., 2021 ; Minnu et al., 2021 ). It is mainly generated via the conventional methods used in the sugar and ethanol agroindustry, which involve storing sugarcane bagasse outdoors for subsequent calcination in boilers.

Conclusions

The following conclusions were drawn from the study on producing finely ground bagasse fly ash and its application in pastes and mortars. The chemical composition of the bagasse fly ash was suitable for use as a supplementary cementitious material, largely because of the presence of 24% amorphous silica and low loss on ignition (2.8%). Moreover, the ashes showed increased pozzolanic activity with a decline in particle size, resulting in accelerated hydration in the initial hours and greater long-term compressive strength of the mortars. A good correlation was observed between packing density and ash particle size, with finer ash resulting in higher mortar packing density. Thus, finer ash exhibited the best mechanical performance, although adequate ash can be produced with D50 of 20 μm. In terms of durability, the acid-attacked M-REF specimens experienced greater mass loss during sulfuric acid attack. However, given the different degradation mechanism of the attacked mortars containing SBFA samples, water absorption increased and compressive strength declined when compared with their nonattacked counterparts and the attacked reference specimens.

In summary, while the use of ultrafine bagasse fly ash in cementitious materials offers several advantages, such as enhanced mechanical performance, accelerated hydration, and environmental benefits, there are also limitations related to durability and mechanical performance with coarser particles. Overall, proper consideration of these factors is necessary for effective large-scale use of sugarcane bagasse fly ash in cementitious applications. Further research should focus on (i) understanding the long-term performance of cementitious materials containing bagasse fly ash; (ii) performing life-cycle assessments to evaluate the environmental impact of using bagasse fly ash as a supplementary cementitious material compared to conventional materials; (iii) investigating the economic feasibility of incorporating bagasse fly ash into cementitious materials, including cost-benefit analyses and assessing the potential for commercial-scale production. By addressing these research directions, further advances can be made in harnessing the potential of bagasse fly ash as a sustainable and effective supplementary cementitious material, contributing to the development of eco-friendly construction practices.

Abstract

Supplementary cementitious materials (SCM) are alternative to the conventional cement and have been studied by so many authors owing to the high carbon content of cement. The use of SCM is significant in addressing challenges of carbon emission and its impact on the 2050 carbon reduction RoadMap. Available studies shows that SCM obtained from both industrial and agricultural wastes presents significant variability in performance as cement dosage in concrete increases. The first aim of this study is to map and synthesize the available evidence from literatures to support this variability. The second objective is to provide statistical evidence from available literatures of certain SCM that enhance the structural performance of low carbon concrete in terms of compressive strength. From the results, trend of findings from literatures on the use of SCM shows a surge in research for cement replacement occurring over the last decade with optimal performance for industrial waste SCM shown to be limiting at 40% cement replacement while that from agricultural waste occurs at 10% cement replacement. Data were sourced from Scopus database and selected from peer review journals of both primary and secondary studies on cement replacement materials. 728 published articles were obtained from the search using four strings namely,’Recent cement* replacement and cementitious materials’’, ‘’Recent supplementary cementitious materials’, ‘’Eco-friendly and cementitious materials’’ and ‘’Low carbon intensive cement replacement materials’. Meta-analysis is carried out on the selected articles having quantitative data to synthesise some of the result of the published articles to examine the impact of Ground granular base slag and Pulverized Fuel Ash cement on concrete strength development as cement replacement. It is shown that Ground granular base slag, Pulverized Fuel Ash and Metakaolin improve and enhance the eco friendliness of the concrete. From the results, optimal percentage of cement replacement is a gap which remains unresolved due to mineralogy and reactivity of the SCMs and would provide the solution for the desired green concrete optimization. It is shown with statistical evidence from meta-analysis that ground granular base slag and Pulverised fuel ash decreases the effect of low compressive strength by at least 2% to about 75% which is considered in our opinion as effective to enhance the sustainability of concrete.

Introduction

The negative impact of cement in concrete on the environment has aroused the need for an alternative solution by using SCM to produce low carbon concrete. Result from literatures indicates that the performance of low carbon concrete is influenced by the type of SCM materials used as well as the percent cement replacement. Guidelines and procedures on the dosage of SCM for effectiveness in low carbon concrete requires that careful selection of materials be carried out with the use of systematic reviews and meta-analysis. The efficacy of research interventions with the use of systematic reviews and meta-analysis to establish guidelines in clinical practice has been demonstrated in the health care [1]. The 2050 Roadmap developed by the international Energy Agency and World Business Council for Sustainable Development considered reduction in rise of global warming to 2 degrees through the reduction of carbon emissions. This implies that emissions from cement manufacture should be reduced by 2050 compared to its current level in view of global energy demand between 12 and 23%. To attain the 2050 target, the use of waste materials as SCM is emphasized for low carbon concrete production [2,3]. In view of the role of concrete for the implementation of United Nation sustainable Development Goals (SDGs) for sustainable housing, there has been a surge in the interest of researchers for sustainable concrete which made it necessary for a thorough and careful application of evidence-based materials selection for cost effectiveness and sustainability [4,5]. These myriads of research are conducted across locations with different methods, materials and at some point, occurring at the same time which could induce repetition, bias, and lack of updated information on the status of an intervention. For this reason, other field of study encourages collaboration and synergy in the form of protocol registration. This is evident in the field of medicine with the Cochrane Collaboration and in social welfare, education, crime, and justice with the Campbell reviews [6,7]. Such collaboration is not seen in the areas of concrete research considering that concrete is the second most used materials after water [8] and its place in addressing vision 2050 target for zero carbon emissions [9], hence the need for systematic review and meta-analysis of cement replacement materials. Unfolding of a research gap in any field of research is based on the extent to which the previous boundaries of research can be expanded with a view to answer research question. This requires building a solid foundation on the discovered body of knowledge through literatures reviews of existing findings in comparison with similar contextual reviews

Conclusion

The widespread use of agricultural and industrial waste as cement replacement materials has affirmed the viability of emerging alternative cement materials for which potentials can be sustainable and durable. The desire for low carbon concrete evident due to its impact on the environment requires a compressive search owing to the fact the performance of cement in concrete has stand the test of time meeting all set criteria of performance except that of sustainability. Due to the huge demand on sustainable low carbon concrete, the mere performance of concrete in terms of compressive strength is no longer a sufficient metrics to measure its performance hence it has been supplemented using recycle industrial and agricultural waste to account for eco friendliness, economy, and sustainability.

• Mechanical properties of SCMs from industrial waste from same source as shown in the combination of gypsum and PFA exhibit poor performance due to variability in density and mineralogy. The chemical composition of PFA at CaO (24.5%) compared to gypsum at CaO (37.7%) and SiO2(35.2%) for PFA while that of gypsum (4%) presents more of a cementitious material than the latter from which its mechanical strength is based. As the cementitious properties of SCMs is dependent on high CaO composition and pozzolanic nature exhibited with more of SiO2. The ratio of CaO/SiO for PFA is 0.69 and that of gypsum is 9.425. The performance of the concrete with a blend of PFA and gypsum resulted to performance owing to high CaO/SiO2 ratio which culminated to its poor cementitious composition.

Abstract

Sustainability is a primary concern that needs to be addressed since infrastructure development requires significant natural resources. Using Recycled Concrete Aggregates (RCA) for road construction has numerous benefits in saving natural resources and the environment. In the present investigation, the demolition waste is being used for road construction, partially/fully replacing natural aggregates. The Cement Treated Recycled Concrete Aggregate (CTRCA) specimens were prepared at 3%, 5%, and 7% cement with various blends of RCA and Natural Coarse Aggregates (NCA) ranging from 0 to 100%. The strength characteristics in terms of Unconfined Compressive Strength (UCS), Flexural Strength (FS), Elastic Modulus, Indirect Tensile Strength (ITS) and durability tests were conducted on cured samples. Microstructural analysis using Scanning Electronic Microscope (SEM) revealed that the pores and cracks in the old mortar have a detrimental influence on the mechanical properties of CTRCA mixes. However, Energy Dispersive Spectroscopy (EDS) and durability tests have shown positive results. The Response Surface Method (RSM) was utilised to optimise the RCA and cement content in CTRCA mixes. The research resulted in the maximum possible RCA of up to 70% with a cement content of 5.8%, which met the Indian Road Congress (IRC) specifications for Cement Treated Bases (CTB).

Introduction

The demolition waste generated from old structures is inevitable due to economic development and technological advancement. More than half of global demolition waste comes from China, India, and the United States of America, with concrete waste accounting for up to 67% of total demolition waste (Chung and Lo 2003, Akhtar and Sarmah 2018). Every year, more than 6 billion tonnes of concrete is produced worldwide (Ä et al. 2012). This waste is disposed of in dumping yards, water bodies, drain trenches, and untilled grounds around human habitations.

Furthermore, accumulating demolition waste in landfills tends to inhabit vacant land that could have been used for other purposes. These waste materials have become vital resources increasingly in road construction due to the scarcity of natural resources. Recycling aggregates from construction and demolition waste is the sole solution to conserve traditional aggregates and safeguard the environment. The potential application of RCA in base and sub-base pavement courses will solve disposal problems and conserve natural resources (Leite et al. 2011, Arulrajah et al. 2014). It is necessary to characterise RCA before its use in pavements. A crucial factor influencing the performance of pavements is the particle size distribution. Different crushing techniques and the concrete’s strength are responsible for the variances in the particle size distribution of RCA (Aydilek.pdf n.d., Arulrajah et al. 2012, Gabr and Cameron 2012). The density of RCA is lower than NCA because of the attached mortar content on its surface (Tang et al. 2018).

Conclusions

In this study, the optimisation and characterisation of the CTRCA mixes were carried out. The RSM was employed to study the effect of individual and combined factors on CTRCA mixtures. Based on test results, RCA can be used in cement-treated base and sub-base courses in Pavements. The following conclusions are drawn based on the present investigation in the laboratory.

. The mix with NCA could get the required strength in UCS, FS, ITS and Elastic Modulus at 5 per cent Cement content after seven days of curing. It also passes the durability test.

. The CTRCA mix with 30 per cent NCA and 70 per cent RCA could get the required strength with 5.8 per cent cement after seven days of curing in terms of UCS, FS, ITS and Elastic Modulus. All the samples satisfy the durability test.

Abstract

Keywords

1. Introduction

2. Experimental design

3. Results and discussion

4. Conclusion

5. Data availability

Declaration of Competing Interest

Acknowledgments

References

Abstract

Sustainability in the construction is becoming a major challanges due to the depletion of natural resources and the avialibility of landfill capacity. Additionally, there is an urgent need to improve the properties of concrete and produce environmentally friendly green concrete. From these points, the effect of varying the water-to-cement (w/c) ratios and the soaking time of glass powder (GP) on the activation of the pozzolanic reactivity and the mechanical properties of green concrete were examined. Two w/c ratios (0.6 and 0.7), two glass contents (5% and 30%), and six GP soaking times werer used in this study. The new mixing method (NMM) was used, in which the GP is partially dissolved in water and more Na+ ions than Ca+2 are formed in solution since Na+ ions have higher mobility than Ca2+ ions. The results indicate that greater normalized compressive strength (CS) is achieved under a w/c ratio of 0.7 for 5% and 30% GP content with soaking time of 6 h. This increase is correlated with the formation of more nucleation sites due to the growth of calcium silicate hydrate rather than portlandite. The relative activation index calculation showed that the 30% GP mixes have higher values than 5% GP mixes.

1. Introduction

Sustinable use of natural resources and effective waste utilization in green concrete is becoming increasingly necessary as natural resources become more limited. Further, the exponentially demand of individual habitaion has led to increased demand for new construction. Fabricating new bottles, flasks, or other tools from glass waste is infeasible due to the amount of energy required (collection, transportation and melting). Therefore, researchers have aimed to reuse crushed waste glass or glass powder (GP) as an aggregate in concrete or as a replacement for cement. The amorphous structure and chemical composition of GP and some types of ash are similar to those of cement, and thus induce a similar pozzolanic effect in concrete. The pozzolanic reaction involves the consumption of the weaker portlandite (CH) to produce calcium silicate hydrate (C-S-H), which has a higher CS and density [1–4].

The traditional or conventional mixing method (TMM), in which GP and water are directly mixed into the concrete mixture, has been used extensively to investigate the effect of using GP in concrete [5]. In the new mixing method (NMM), the GP is presoaked in water to partially dissolve it before it is mixed into the concrete mixture, thus activating the pozzolanic reaction earlier in the life (at 90 days for concrete made with TMM) of the concrete via hydrolysis of the GP and producing stronger concrete than the control [6,7].

The mechanical properties of fresh and hardened concrete using GP depend on the chemical composition, the diameter of the GP particles, and the curing conditions [8,9]. The mixing method used also contributes to the mechanical properties; the NMM allows for the partial dissolution o

A comprehensive review of the statistical experimental optimization problem concerning the mixture design of various cement-based materials is presented herein. This review summarizes and discusses over 80 applications of optimum design regarding the basic test information under response surface method (RSM), including influence factor and corresponding response, statistical method, and coefficient of determination. The statistical experimental design reported in previous studies has shown that RSM is a sequential procedure to provide a suitable approximation for the mixture optimization. Then, linear, quadratic and interactive relationships of the statistical model can be evaluated available. Especially, the multi-objective optimization issues with multiple or competing performance requirements for various cement-based materials have also been reported, by considering fluidity, strength development, environmental impact, cost and durability. Overall, the results from existing publications have demonstrated that statistical inference and analysis of variance (ANOVA) are suitable for mix proportion design and process optimization of cement-based materials. The W/B ratio and mixture components are the prevalent factors in experimental design optimization, and then the fluidity and strength as the most popularly used response. Thus, theoretical optimum mixture proportioning can be used to predict valuable fresh and hardened properties. Finally, a critical discussion of the selection of design strategy, independent factors and their responses, and the experimental region involved in statistical experimental design, is provided. Based on this review, we conclude that the multi-objective optimization approaches need a further systematic study, and further studies of sustainable concrete optimization are needed by comparing the different chemical composition and particle characteristics.

1. Introduction

The cement-based materials are prepared by using various types and quantities of individual constituents. These mixture proportions play an important role in fresh- and hardened-state performance, such as fluidity, rheological properties, strength development and durability. Therefore, many research studies have been dedicated to experimental optimization of cement and concrete mixtures.

1. Introduction

2. Materials and methods

3. Results and discussion

4. Conclusions

Abstract

This study aims at investigating the possibility of using smectite clay waste, generated during the oil bleaching process as an additive for Portland cement. The smectite clay waste consists of montmorillonite, quartz, anorthite, calcium sulfate, and amorphous phase. For the regeneration of this waste, the extraction with hexane and thermal method were chosen. The results showed that the extraction of smectite clay waste with hexane significantly increased the pozzolanic activity of this waste; however, the extracted additive prolonged the induction period of Portland cement hydration, slowing down initial cement hydration, and reduced the compressive strength of Portland cement samples.

The thermal activation method achieves the best results by calcining smectite clay waste at 600 °C. The calcined additive indicated the strong pozzolanic activity. However, this phenomenon is associated with the formation of the amorphous phase by activating the smectite clay with the sulfuric acid rather than the degradation of the clay minerals during the combustion. The calcined smectite clay waste (CSCW) accelerates the hydration of calcium silicates in the second period of the exothermic reaction. The results of the investigation showed that in samples with the CSCW additive proceed the intense pozzolanic reaction, which can be clearly identified after 28 days of hydration. Up to 15 wt% of the Portland cement can be replaced by the smectite clay waste additive calcined at 600 °C without reducing the compressive strength of Portland cement samples.

Introduction

Nowadays one of the most current issues is the environmental pollution caused by industrial waste, which is being produced by large-scale production in various industries. Only a small part of the industrial waste is recycled and its application in other industries is highly important. Various studies have shown [1-5] that some industrial waste can be used by replacing a part of the clinker in cements or a part of the cement in concrete. In this case, when the waste is used as an additive for 32 binding materials, not only the pollution issue is solved but also the cost of Portland cement or concrete is decreased.

Oil bleaching is one of the processes applied in oil industry during which the impurities that add colour to the oil are removed and oil is purified from carotenoids, peroxides, chlorophyll, etc. Oils are bleached using a powdered, surfactant materials, which are called bleaching earths. Bleaching earths can composed of up to different types of clay minerals, such as smectite, bentonite, attapulgite and sepiolite. The bleaching process is carried out under vacuum, with temperature in the range of 80-120 °C and contact time ranging from 20-40 min. The dosage of bleaching earth usual is 0.5-2 % by weight. After bleaching, the mix of clay and oil are separated by the vacuum filtration into two phases: oil and clay waste. As a consequence, the oily clay becomes hardly recycled waste. Market demand for activated bleaching earth was predicted to rise to ~9M/year tones until 2022, therefore, the amount of waste produced through the edible oil bleaching process, is considerable [6].

Engineered Cementitious Composites (ECC) is a typical High Performance Fiber Reinforced Cement-based Composite (HPFRCC), which possesses the characteristics of ultra-high tensile ductility and energy dissipation capacity. One of the potential applications of ECC is to replace conventional concrete in the seismic resistant structures. However, to date, the investigation on seismic performance of ECC at the structural level is still limited. This paper aims at evaluating the seismic performance of RECC frame on the basis of Performance-based Seismic Design (PBSD) concept and discussing the feasibility and practicability of applying ECC in structures for improving the seismic performance. The non-linear behavior of ECC material was simulated especially considering the strain hardening behavior in tension. By using the Incremental Dynamic Analysis (IDA) method, three types of frames, consisting of a normal RC frame, a RECC frame and an RECC/RC composite frame, were analyzed to evaluate the structural dynamic behavior of the frames. Comparative studies on the deformation limit states at five levels of seismic performance for these three different types of frames validated that RECC frames have superior deformation capacity comparing to traditional RC frames under high intensity earthquake. Comparison results also indicated that rationally applying ECC in key region of the structures can not only improve the seismic performance and deformation capacity of structures but also control the construction cost.

Introduction

Engineered Cementitious Composites (ECC), generally consists of cement, mineral admixture, fine aggregates, water, admixtures which are used to enhance the strength and workability, less than 2% volume of short fibers, was first developed by Li et al. [1–3] based on the basic principle of micromechanics and fracture mechanics. Different from normal concrete with brittle tensile behavior and crack localization, ECC exhibits multiple fine cracks and strain-hardening behavior under tension. The opening of each crack is usually controlled to be less than 100 μm, and the ultimate tensile strain can reach over 3.0% [4–6]. A typical tensile stress-strain relationship of ECC is shown in Fig. 1. The ultra-high tensile ductility and energy dissipation capacity of ECC just remedy the shortcomings of concrete and thus attract the attentions of many researchers and designers around the world. ECC is being considered for replacing conventional concrete in structures in high-intensity earthquake regions [7–9]. Research efforts have focused on the seismic related behavior of ECC [10–18], however, the researches with respect to ECC are mostly limited to the material level and component level, while the investigation focusing on ECC at structural level is still at the preliminary stage. Gencturk et al. [19–20] established a constitutive model for ECC within Zeus-NL, and a two-story-two-span frame was simulated with the proposed model and tested under dynamic loading.

Deterioration of cement/casing adhesion in wellbore scenarios can result in unwanted and potentially harmful leakage with the potential of serious repair costs. In this work, the authors explore the use of self-healing polymers added to conventional wellbore cements as a way to bring about self-healing and readhering (to casing) properties to the composite. Self-healing capability was demonstrated by permeability analysis showing that polymer-cement composites reduce flow by 50–70% at cement bulk and at the cement/steel interface. Use of atomistic simulations imply that these polymers have good wetting properties on the steel surfaces. Interactions between steel/polymer and cement/polymer are complementary, resulting in a wider range of bonding patterns. Cracks seem to expose under-coordinated sites that result in more bonding interactions, which agrees well with the permeability measurements showing high degree of healed cracks and cement-steel interfacial gaps together with an overall increased in structural integrity of these advanced polymer-cement composite materials.

Introduction

Wellbore integrity is a significant environmental consideration in industries which use deep production wells such as in geothermal energy production. During wellbore construction, cement and cement composites are injected into the annulus between the geologic formation and the wellbore casing to hydraulically isolate production zones from overlying aquifers[1]. When applied using strict industry standards, cement and cement composites can extend the life of a producing well as well as protect the near surface environment. The potential for short life of wells and expensive remediation costs can hinder the development of geothermal energy despite of the fact that a large number of reserves of this clean energy alternative exist in the United States and around the globe[2]. A study of over 380,000 wells worldwide found that nearly 7% of wells experience wellbore failure[3] with one of the main reasons being the high temperature  (up to 400 °C), thermal cycles, and chemically corrosive (typically hypersaline, CO2 and H2S rich) environments[4] typical of low and high temperature geothermal systems. Failure of the wellbore cement can be due to a combination of chemical degradation, fracturing, and deboning from the host rock or well casing. Wellbore integrity issues are most common in the form of leakage pathways allowing for unwanted fluid migration. Cement bonding to the interface of both the casing and host rock has been identified as one of the most significant wellbore integrity issues[5].

1- Introduction

2- Current state of knowledge

3- Materials and methods

4- Results and discussion

5- Conclusion

References

Abstract

In the case of massive concrete structures, the heat generated by cement hydration may cause cracking due to thermal strains. The mix design of the concrete used for such structures has to take account of mechanical properties and generated temperatures. Using experimental design principles, the hydration heat and the development of compressive strength are measured in order to determine how the composition of concrete and the presence of SCM influence the characteristics of concrete and to create a mix design protocol. This protocol can help to determine which mix design minimizes the hydration temperature for a given compressive strength.

Introduction

In massive structures, the exothermy of the hydration reactions of cement and the thermo-hydro-mechanical behavior of early age concrete can lead, if strains are restrained, to the development of compressive and tensile stresses. If the tensile stresses exceed the tensile strength, cracking may occur, threatening the durability of the concrete. In order to prevent the risk of cracking as well as that of Delayed Ettringite Formation (DEF), sulfate resisting cement and the use of additions are recommended [1]. Mineral additions such as limestone, slag or fly ash can also be added to concrete to decrease the exothermy of hydration reactions and, in the case of slag and fly ash, protect against DEF. The aim of this research is to obtain a tool which optimizes concrete mix design while respecting classical specifications such as the compressive strength after 28 days and minimizing the temperature rise in massive structures. To do this, the impact of several parameters of cement (composition and fineness) and of concrete (type and percentage of additions, W/B ratio, chemical admixtures) on the rheology, hydration heat and mechanical strength of concrete have been studied by means of an experimental design. The influence of the different factors is analyzed and a concrete mix tool is proposed. Finally, this tool is applied to the case of massive concrete structures.

1- Introduction

2- Materials and methods

3- Results and discussion

4- Discussion

5- Conclusions

References

Abstract

In this study, the influences of ultrasonic and surfactants on the dispersion of graphene sheets in water were evaluated using UV–vis spectroscopy, and homogenous dispersions of graphene sheets in water were obtained by using sodium dodecyl benzene sulfonate (SDBS). Then, the highly dispersed graphene sheets were introduced to cement paste through high-speed mixing, and the mechanical and microstructural properties of graphene-modified cement material was evaluated. Experiment results indicated that the addition of 0.025 wt% graphene sheets increased the 7-day composite compressive strength by 14.9%, the flexural strength by 23.6% and direct tensile strength by 15.2%. X-ray diffraction (XRD) analysis showed that the addition of graphene sheets lowered the orientation index of calcium hydroxide (CH) crystals significantly. Moreover, mercury intrusion porosimetry (MIP) and microscope imaging (SEM) indicated that a high degree of dispersion of graphene sheets was achieved, and the two-dimensional graphene sheets promote hydration and suppress the extension process of cracks.

Introduction

As a main component of concrete, cement is the most widely used binder material in the world. However, one of cementitious materials’ biggest drawbacks is their quasi-brittle nature and poor resistance to crack formation. Thus, many studies have been carried out to combine nano-fiber with cementitious composites to enhance their microstructure and mechanical properties, and results showed a small amount of carbon nanotubes (CNTs) can restrain the propagation of microcracks and improve the fracture toughness of the nanocomposites [1–3]. However, CNTs tend to agglomerate, hindering their dispersion in solvents because of their super high length-diameter ratio [4]. As a two-dimensional nanomaterial, graphene is the basic structural element of other allotropes, including graphite, CNTs and fullerenes [5,6]. The theoretical specific surface area (SSA) of graphene can reach 2630 m2 /g, which is much larger than that reported to date for CNTs [7]. In addition, it has an intrinsic tensile strength of 130 GPa and a Young’s modulus of 1 TPa [8]. Due to its remarkable mechanical performance, great attention is paid to the graphene as the nano reinforcing material in cement with greatest potential. Development of aqueous dispersions incorporating higher concentrations of graphene sheets would facilitate scalable production of graphene sheets modified concrete [9]. Thorough dispersion of graphene sheets in water is the key first step toward achieving uniform dispersions of graphene within cementitious composites [10]. Different surface treatments have been investigated for improving the hydrophilic property of graphene. Current processing methods involve acid treatment [2], oxidation via heating [11], ozone treatment [12] and silane treatment [13].

With the development of urban infrastructure, subway and other underground projects are gradually being constructed in various cities. The influence of water absorption on surface of cement-based materials has therefore become more and more important. A mathematical model and the relative experiment of water absorption in cement mortar were investigated. The results showed that the change of radius of pore was decreased and absorption mass fraction was increased with the increased of absorption time. The possibility and direction of reaction during this process were studied, and the result showed that hydrolysis was not merely occurred in this process.

Introduction

Cement-based material is one of the most useful materials in civil engineering. Based on the characteristic of porous of cement-based material, its service performance change accordingly. When they are built in the underground environment, water tends to penetrate cement-based materials as capillary force. Because of existence of other ions in groundwater, it penetrated into the materials and lead to be affected of durability of materials. Therefore, the research of absorption of underground water on surface of cement-based materials is important. The recent research of absorption behavior was mainly focused on the fitting equation. the fitting method was adopted in the research of Martys et al.

The flexural properties and impact resistance of the composites with bamboo cellulosic fiber (BF) weight fractions ranging from 4% to 16% was investigated using a universal testing machine and a full instrumented drop weight impact system, respectively. The effect of addition of BF on the flexural properties and impact resistance of the composites was estimated according to max flexural strength, fracture toughness, the contact force, failure pattern and absorbed energy. On the basis of the above results, the impact behaviour of the specimens with 12 wt% BF was examined from the point of view of the impact energy change, the deformation feedback and the absorbed energy. Additionally, impact damage morphology and extent were analyzed using the digital camera and an industrial microfocus computed tomography (CT) system. The results show that BF reinforced cement based composites have higher fracture toughness and impact energy absorbility, the fracture toughness and absorbed energy of the specimens with 4–16 wt% BF are higher by 2.7–45.9 times and 2–24 times than that of the control specimen, respectively. However, due to fibers agglomeration resulted from fibers addition beyond certain content, max flexural strength and impact resistant of the composites no further increase. Furthermore, the different impact energy leads to the different failure patterns and energy absorption modes: at low impact energy, the main energy absorption modes are the debonding between fiber and the matrix; with the increase of the impact energy, the main energy absorption modes are delamination and BF breakage.

Introduction

In recent years, utilization of natural fibers in cement based composites has attracted increasing attentions, due to their many advantages over traditional fibers, such as biodegradability, economical and eco-friendly, etc. [1–5]. And natural fibers have already been considered as potential alternatives to traditional fibers (steel fiber, polymer fibers, glass fiber) [6]. Many studies in previous references have reported the influence of natural fibers on the properties of cement based composites, such as flexural properties [7–9], crack resistance [10,11], durability [12–14] and impact resistance [15–17], and the results show addition of the natural fibers can remarkably improve the toughness of the cementitious materials. Generally, the capacity of absorption energy of the composites is defined as ‘‘toughness”, which is very important for evaluating the service behavior of composite materials under actual conditions when fibers reinforced composites are subjected to static, dynamic or fatigue loading [15]. It is well known that the impact test is a method to evaluate the toughness and ductility of cement based materials [18], while the impact strength is a specific parameter to measure the toughness of materials under dynamic impact loading.