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

Corrosivity category of the atmosphere in coastal regions is usually very high. Reinforced structures frequently show short service life if adequate measures are not applied. Determination of time-to-corrosion-initiation (ti) and time to corrosion with induced cracking (tcc) to calculate the service life in buildings located in coastal cities is not usually performed. Changes in ti and tcc, depending on the w/c ratio, and concrete covering thickness, were determined in extremely aggressive coastal outdoor exposure site located within 10 m of the shoreline in Havana, one of the most aggressive coastal sites in the world. The electrochemical corrosion rate was determined in the reinforced concrete specimens. It is a very important parameter to follow environmental degradation of concrete. Environmental parameters were determined at the site. Calculated Chloride deposition rate is over the maximum level established in ISO 9223 standard (S3). Effective capillary porosity, compressive strength and ultrasonic pulse velocity were determined for all specimens. An acceptable service life was obtained for w/c ratio 0.4. However, effective capillary porosity is an important parameter to determine the concrete quality assessment before building reinforced structures exposed to extreme corrosivity. It is recommended to consider this parameter to predict a service life in very aggressive coastal sites.

Introduction

Many reinforced concrete (RC) structures located in coastal cities and exposed to the direct influence of marine aerosols present generally a severe deterioration, indicative of short service life (Sl), caused mainly by atmospheric corrosion of the reinforcement steel [1–4]. The RC structures are often built using very permeable concretes with low quality.

Different softwares (Life-365, Eucon, and Duracon/fib MC SLD) have already been developed to calculate the Sl of RC structures in coastal cities [5]. Some input basic parameters as cement type, concrete constituents, water/cement (w/c) ratio, additions, air content, concrete covering thicknesses, and protective systems, play a fundamental role in the determination of Sl. However, some input basic parameters depending on concrete quality as effective capillarity porosity, compressive strength, ultrasonic pulse velocity, and behavior of electrochemical corrosion rate in the reinforcement steel are not included in the software. Atmospheric transitory processes such as chloride deposition rate, relative humidity, and wind speed influencing in the corrosivity category of the atmosphere, and in the electrochemical corrosion rate in the reinforcement steel, neither are included in the software as input basic parameters [6, 7].

Conclusions

The Sl of RC structures in extremely coastal site of a city like Havana, considered one of the most aggressive environments of the Ibero-American region, depends on concrete quality, and atmospheric corrosion of reinforcement steel. Changes in the w/c ratio and concrete cover thickness, determined significant changes in the atmospheric corrosion rate of reinforcement steel in RC specimens exposed to extreme (CX) corrosivity categories of the atmosphere. The role of concrete cover thickness with respect to the Sl in RC structures become important for 0.4 w/c ratio.

Prediction and determination of the Ic, as indicator of atmospheric corrosion of reinforcement steel bars in RC specimens exposed in a coastal outdoor exposure site, can be used to obtain ti plus tcc. The importance of obtaining ti from the prediction and determination of Ic in the reinforcement steel is confirmed in the research work.

Abstract

The marine environments reduce the working life of the concrete structures owing to the severe exposure to the chemical ingress, and continuous contact with the humid air, and saline soil conditions. A scientific investigation and the conditional assessment of the existing structures may be helpful to learn the damage mechanism. This article represents the scientific conditional assessment of some existing old concrete structures in the coastal areas of Jamnagar and Dwarka of Gujarat. The objective of the study was to collect information on the types and severity of the damagesin the existing structures and preparing an assessment rubric mentioning the significance of modes of marine environment resulting in a specific damage type. To evaluate the severity of the damages, the parametric approach and a root cause analysis including the experimental investigations on the collected samples has been utilized. The outcomes revealed several interesting observations those have been classified into three major attributes namely material limitations, structural design and third as the gross environmental impacts. The study encouraged the authors to dig deeper in the area of work and showed potential of the methodology to understand the damages caused by the marine environments to the on-shore concrete structures.

Introduction

The marine exposure condition imposes a challenging environment on concrete as a material, structures and member. The long-term performance of concrete in marine environment is observed to be subjected on a complex integrated physical and chemical mechanisms [1]. The marine environment is not always regarded as the sea water, but it is the combination of the marine sand /ground, air and temperature at and around the coastal regions and the shallow as well as deep sea water together. In such cases, the damage occurred on the concrete structures needs to be evaluated or assessed for the damage with a systematic approach. Therefore, conditional assessment of the marine structures is merely not similar to the other structures. In fact, how to assess the damages of concrete in marine environments is a challenge because the nature of degradation and skill of damage varies with the location of marine structure. The concrete in the marine environment along with the reinforcements of steel bars shows damages namely corrosion, efflorescence, staining, erosion, cracking, mortar spalling and surface losses, lump mass losses, and many others. Regarding reinforced concrete in particular, chloride ingress by diffusion is probably the most important mechanism of deterioration, leading to corrosion of the embedded reinforcing steel. However, the overall situation is complicated by concomitant deterioration of the material itself by sulfate attack and physical effects such as salt crystallization and mechanical action of the waves.There are references available to refer on the topic of assessment of damage in marine environments. Use of common methods of assessment includes use of rebound hammers, porosity meters, carbonation tests on the samples [1] providing preliminary damage information, use of non-destructive tests methods and visual inspections [2], [3], on site assessment of the strength parameters of the concrete [4], use of permeability apparatus for fluid ingress, destructive tests on samples at the site and chemical analysis of the samples in laboratories [5], [6], assessment of the degree of the distresses in the concrete due to marine environment by visual and analytical inspections of the sites [7], applications of electromagnetic methods on the existing structures [8], the corrosion detection of the damages structures in the repaired structures by.

Conclusion

From the case study and the proposed systematic assessment methodology, the authors have observed that the conditional assessment of a marine structure requires a panoramic perspective on the investigations. The site survey remains the key factor for obtaining the exact details of the structural conditions, however the pre-assessment survey and related inquiries supports the process significantly. The laboratory tests and results contributed to a significant extent in ascertaining the scientific reasons for the damage. The study encouraged the authors to propose an overall severity rubric based on the systematic assessment process suggested in the present study. Table 4 indicates the overall rating to be utilized for declaring the damage scenario of the structures impacted by the marine environment.

Abstract

Concrete exposed to splash zone in partially submerged concrete structures deteriorates rapidly due to reasons such as wetting-drying cycles, the impact of waterborne materials, bio-deterioration, chloride and sulphate attacks. Existing condition assessment and rating systems do not adhere to the interrelation between different performance attributes of splash zones and these models are extremely subjective to the performance of the evaluator. The objectives of this study are to evaluate the effectiveness of parameters that deteriorate marine concrete structures and to develop a new model to predict the rate of deterioration of splash zone in marine concrete structures. The fuzzy Analytical Hierarchy Process (FAHP) was used to develop the model to predict the rate of deterioration. Here, local factors were grouped under five primary parameters as visual inspection, water quality, casual factors, Non-Destructive Tests (NDTs) and crack details. Data relevant to 15 structures were gathered by visual inspection, laboratory and field experiments to validate the proposed model. Attributes of water quality achieved the highest priority for the deterioration of the slash zone of marine concrete structures. Further, numerical values were assigned to this rating model to avoid ambiguity and vagueness of linguistic descriptors in existing rating systems. Finally, the model developed in this study can be used to evaluate the deterioration percentage of the splash zone in structures and according to that appropriate retrofitting and repair work can be done.

Introduction

At the present, reinforced concrete has been widely used in coastal and underwater structures in order to construct bridges, jetties, breakwaters and floating structures. However, concrete is more prone to deteriorate due to the aggressive environmental conditions in the atmospheric and splash zone due to chloride content in water, sulphate attacks, abrasion erosion caused by slit, sand and gravel, wetting and drying cycles and due to presence of waste and chemicals in water [13], [5]. These environmental parameters will cause cracking, spalling and corrosion which leads to incurring an enormous amount of money on repairing purposes and also this will reduce the structural health and safety of structures [23].

According to researchers, deterioration of concrete structures due to chloride induced reinforcement corrosion is a major problem around the world and reinforcement in partially submerged concrete structures is mainly corroded due to the ingress of chloride ions [18], [39]. According to Neville [20], a protective oxide layer that consists of γ-Fe2O3 is formed on steel which is generated soon after the hydration of concrete has started. Chloride ions that ingress inside concrete can be dissolved in pore solution (free chloride) or bound to the cement hydrates (bounded chloride) and only free chloride contributes to breaking this passive layer which results in corrosion [17]. When the concentration of chloride ions in the pore solution around the steel surface reaches the threshold value this film will be destroyed [4].

Conclusions

In this study, a rating model was developed to predict the rate of deterioration of the splash zone of marine concrete structures and the model was validated by assessing the current condition of 15 existing marine concrete structures. The model was developed based on FAHP and numerical definitions were used to avoid subjectivity of evaluators. According to the model, water quality has the highest priority for the deterioration of the splash zone of the structure and visual inspection, causal factors, crack detail and NDT have priority weights in the decreasing order. The proposed method can be used to rate the deterioration percentage of existing marine concrete structures in tropical countries and according to the results obtained from the model, proper remediation can be done. As future research work in this domain, freeze-thaw action can be taken into consideration in order to modify this model.

This study aimed to investigate the influence of low temperature ranging from 20
C to 0
C on the compressive strength and pore structure of a certain pile foundation concrete in the permafrost regions in China. This study analyzed concrete microstructure by low-temperature SEM. To quantify the influence of freezing amount, the relationship model of the compressive strength of concrete in a low-temperature environment was established based on the theory of accumulative curve of liquid saturation. Compressive strength increased with decreasing temperature. This finding was due to the gradual decrease in the pore radius of the water–ice phase transformation of concrete, and the amount of ice increased. This condition forms a complete and compact ice body and concrete bond, which gradually reduces concrete porosity. The calculated value of concrete compressive strength model established under pore icing is consistent with the experimental value.

Introduction

The Qinghai-Tibet Railway, also known as the ‘‘Road to the Sky,” crosses the world’s largest distance of permafrost area at 550 km [1]. The average and minimum temperatures in the permafrost area are below 0
C and ranging from 16
C to 20
C [2,3]. The total length of the bridge and tunnel is approximately 8% of the total length of the railway. The pile foundation of bridge engineering has been in the permafrost area for a long time. Thus, concrete is required to reach the design strength under low temperature conditions and permafrost regions. The strength of the pile foundation in the permafrost area is greatly significant to the safe use of the Qinghai-Tibet Railway. Therefore, the strength of the bridge pile foundation structure in the permafrost region in China is studied in this paper. Compressive strength is an important basis for evaluating concrete strength. The strength of concrete exposed to different temperatures from 0
C to 20
C needs to be studied, and the results provide a reliable basis for evaluating the performance of low temperature concrete structure of the pile foundation of the Qinghai-Tibet Railway Bridge Project. At present, concrete is an excellent low-temperature building material [4,5] that has good mechanical properties [6]. For example, Lee GC [7], Hideo Kasami [8], and Chuanxing Wang [9] considered that the compressive strength and elasticity modulus of concrete with different strengths have been improved to some extent at low temperatures (in the range 100
C to 0
C).

1. Introduction

2. Significance of the research

3. Materials and experimental procedure

4. Results and discussion

5. Conclusions

Declaration of competing interest

Acknowledgements

References

Abstract

Alkali-activated concretes are being considered as an alternative environmentally friendly construction materials compared to the ordinary Portland cement. However, although these materials have reported mechanical properties comparable to those of OPC, the corrosion of reinforcing bars is a major durability issue that needs to be studied. This article studies the corrosion performance of an alkali-activated binary reinforced concrete (AABC) based on natural volcanic pozzolan (NP) and ground blast furnace slag (GBFS) exposed to chlorides ions. OPC concrete was used as reference material. To carry out the study, accelerated chloride ingress methods (impressed voltage, wet-dry cycles, and saltwater immersion (3.5% NaCl)) were used. Monitoring of the corrosive process was carried out using the techniques of half-cell potential, linear polarization resistance, polarization curves and curves of current intensity versus time. As complementary techniques, surface electrical resistivity and resistance to chloride ion penetration were evaluated. AABC showed higher resistance to chloride ion penetration compared to OPC concrete, a reduction of the charge passed up to 60% at 360 days of exposition. In general, the various accelerated chloride ingress techniques employed in the present research revealed that reinforcing steel embedded in AABCs have a higher resistance to corrosion compared to steel bars embedded in Portland cement (OPC)-based concrete. It should be noted that the B constant values obtained for AABC differ from the values commonly used in (OPC)-based concretes. In addition, the results indicate that the ranges of corrosion probability, such as half-cell potentials or corrosion currents, specified for OPC concretes should be checked for its application in alkali-activated concretes.

Introduction

Reinforced concrete based on ordinary Portland cement (OPC) is one of the most widely used materials in the civil industry due to its versatility, properties and low cost. One of the most important factors for the construction industry is the durability, which is determined by the useful life of the material under real service conditions, including its exposure to aggressive environments [1]. Durability is not an intrinsic property of a material, since it depends on the conditions of service, so that in concrete it is known to vary according to the type of environment to which it is exposed. One of the biggest threats that reinforced concrete faces is the corrosion of reinforcing steel due to cracking, delamination, and in severe cases, the partial or total collapse of a structure. The primary cause is the exposition to aggressive environments such as CO2 and/or the entry of chloride (Cl−) ions [[2], [3], [4], [5]]. These agents have been responsible for most structural damage and, therefore, a significant increase in investment in structure maintenance and repair. Chloride ions can come from a range of sources – marine environments, the use of de-icing salts (≈NaCl), chemical substances coming into contact with the concrete, or they may be present in the concrete mix, as happens with the inclusion of some types of additives (CaCl2) during production. Chlorides diffuse through the concrete and, on reaching a critical concentration near the steel, cause destruction of the passive layer and initiate the corrosive process, generating pitting corrosion in the steel [6,7]. In addition to concrete durability, a major concern is the environmental impact associated with production, especially relating to the use of Portland cement (OPC). Indeed, the OPC industry generates annually 2 billion tons of CO2, corresponding to 8–10% of greenhouse gas emissions into the atmosphere [[8], [9], [10]]. For this reason, research applied to the development of alternative low carbon footprint cementitious materials is a priority for the construction sector [11]. Among these alternatives, alkali-activated materials (AAMs) have caught attention. These are obtained from chemical interaction between an alumina-silicate material (precursor) and a strongly alkaline solution (activator) [[12], [13], [14]]. AAMs are synthesized at temperatures between 25 and 100 °C, while OPC production temperatures rise to 1460 °C to obtain clinker. AAMs can thus be considered as potential low carbon cements [15]. These types of materials also have structural mechanical strengths and physical characteristics such as reduced permeability and thermal stability [16,17].

Along with the rapid urban development and economic activities, the generation of construction and demolition (C&D) waste has increased substantially in many parts of the world. At the same time, large quantities of natural aggregates are extracted for construction every year [1]. The utilization of recycled aggregates (RAs) in concrete production can potentially conserve the nonrenewable natural resource of natural aggregates, eliminate unnecessary consumption of limited landfill areas and reduce energy consumption. Due to its benefits on preventing the shortage of natural aggregate and the deterioration of ecological environment caused by concrete waste, Recycled Aggregate Concrete (RAC) technology is considered as one of the main candidates for ecological concrete development [2]. However, the variability in the characteristics of RA and RAC prevents the use of RA further. For example, the use of RCA can lead to reduction of up to 40% in compressive strength [1,3]. Low density and high water absorption and porosity, mainly caused by the heterogeneous nature of RA, can influence the properties of fresh concrete and then reduce its workability [4–6]. Over the last two decades, many investigators have made use of various methods to predict the properties of concrete with different components. The compressive strength of recycled concrete is closely related to these factors such as sand rate, watercement ratio, aggregate grade, aggregate type and substitution rate, mineral fine admixture variety and dosage [7,8]. However, the relationship between those factors and compressive strength shows a complex non-linear relationship, and there is still no definite theoretical formula which can accurately reflect their relationships [9,10]. In practice, substantial experiments have to be carried out to ensure the compressive strength of recycled concrete to meet the requirements. Nowadays various artificial intelligence algorithms, such as neural networks (NN) and support vector machines (SVM), are widely used in concrete strength prediction. In [11–13], the artificial neural network serves as to predict the relationship between the different influencing factors and compressive strength of recycled concrete. The nonlinear mapping ability of BP (Back Propagation) neural network is adopted to establish the non-linear model between input variables and output variables. Thus accurate intensity prediction could be realized through a certain training and iteration. A 7-20-3 BP neural network model is employed in [14] to predict the recycled concrete slump. In [15], the neural network model and ultrasonic pulse velocity test are proposed to predict the concrete compressive strength. Although BP neural network shows good abilities on solving non-linear problems, it also exhibits some disadvantages including slow convergence, over learning and local optimization which will affect the accuracy and efficiency of prediction. In [16] the neural networks and the adaptive neuro-fuzzy inference system are combined to improve the capability of prediction model. In [17], artificial neural networks and regression techniques are used to analyses the relations between concrete components and concrete properties.

Non-destructive geophysical methods are effectively used for reducing the damage of concrete and to obtain economic results in terms of time and financial. With these methods, it is possible to detect the faults of the materials during manufacturing or after a certain period of use (cracks due to corrosion or abrasion, voids in the internal structure, reinforcement detection, etc.). Some researches has also been used several methods combined. The problems related to the structure have increased the importance of structure analysis. Some of the main important targets of the structural analyzing investigations by using non-destructive geophysical techniques such as electrical resistivity technique (ERT) is used for determine the electrical properties of concrete and reinforcement corrosion (Feliu et. al., 1996; Lataste et. al., 2002; Polder and Peelen, 2002; Güneyisi et. al., 2005; Ferreira and Jalali, 2006; Sadowski, 2010; Plooy et. al., 2013; Ghosh and Tran, 2015); induced polarization (IP) is used for obtaining information about concrete sample structure (Altundaş, 2010); electromagnetic (EM) is used for determination presence of reinforcement (Zhao et. al., 2014; Moustafa et. al., 2016); ground-penetrating radar (GPR) is used for display of reinforcement fittings in columns and beams, determination of existing building foundation type and discontinuity investigations in columns and beams (Buyle-Bodin et. al., 2003; Sbartai et. al., 2007; Cassidy et. al., 2011); seismic ultrasonic wave technique is used for determine the quality of concrete, internal cracks as well as the deterioration in the concrete and estimation of the concrete strength (Pimenov et. al. 1972; Martin and Forde, 1995; Yeih and Huang, 1998; Naffa et. al., 2002; Kewalramani and Gupta 2006; Lorenzi et. al. 2007; Trtnik et. al., 2009; Uyanık et. al., 2011; Uyanık, 2012; Uyanık and Tezcan, 2012; Uyanık et. al., 2012); Petro and Kim, 2012; Pfister et. al., 2014; Sabbağ and Uyanık, (2016a; 2017)); Schmidt Hammer is used for determining concrete strength (Ergün and Kürklü, 2005; Jain et. al., 2013); microtremor is used for determining the foundation type (Uyanık, (2014; 2015); Uyanık et. al., 2015), dynamic behavior of building (Navarro and Oliveira, 2008), construction period (Timur et. al., 2015) and seismic effects on building structure (Sanches et. al., 2002); radioactivity (RA) is used for the effects of construction materials radioactivity quantities on human health (Uyanık et. al., 2013; Kılınçarslan et. al., 2011; Abbasi, 2013; Akkurt et. al., 2013; Işık et. al., 2017). From among them the impact of reinforcement and curing conditions to the concrete strength can be determined by measuring resistivity of concrete. In this case, valuable data can be obtained without any damage to the structure so as to deal with problems such as the concrete strength of the existing structure and the status of the reinforcement in the concrete.

Generally, there are two main types of specimens used for testing of compressive strength of concrete around the world – cylinders and cubes. Specimens of varying shapes and sizes are preferred in various countries. In the states using European standards (EN), 150 mm cubes and 150/300 mm (diameter/height) cylinders are the most commonly used types. In connection with the advancement of concrete technology and considering wider use of high-strength fibre-reinforced concretes (HSFRC), these types of specimens are often replaced by smaller samples, mainly by 100 mm cubes. The reason why cubes are preferred over cylinders is elimination of bottom and top surface preparation. Cylinder end grinding equipment is expensive, it is difficult to find a capping material with suitable properties for testing of HSFRC. Smaller specimens are also advantageous because of easier handling of the samples and lower material consumption. The main reason why smaller cubes are preferred is the effort to reduce testing machine capacity requirements. According to the experience of the authors, capacity of common testing machines usually does not exceed 3 MN, which means that the maximum possible strength of 150 mm cubes to be tested is 130 MPa. Such value is sufficient for majority of purposes, but not for research and application of the most advanced HSFRC. If the 100 mm cubes are used, the required force is theoretically 2.25 times lower. This enables testing of concretes exceeding 250 MPa compressive strength with the use of the same machine. The situation is similar concerning the flexural strength which is the second most important parameter of HSFRC. Both 150 × 150 × 700 mm and 100 × 100 × 400 mm prisms are exploited in the states where European standards (EN) are adopted. In this case, capacity of testing machine is not an issue. Easier production and handling of the samples made 100 × 100 × 400 mm prisms more common in the recent years (the weight of the sample is approximately 10 kg compared to 40 kg in case of the bigger one), but 150 × 150 × 700 mm prisms are still employed occasionally as some specialists consider them to provide better representation of flexural behaviour of the material in real structure. There is a general agreement on the fact that the results of both compressive strength and flexural strength tests are affected by the size of the sample to some extent. However, opinions regarding the quantification of the size effect are ambiguous. As will be shown in chapter 2.2, various researchers have come to miscellaneous conclusions when studying different types of concrete. In this paper, the authors focused on HSFRC with maximum aggregate size of 16 mm which is the object of their long-term research.