No / Degrading infrastructure and applications of structural demolition create tremendous amounts of construction and demolition waste (CDW) all around the world. To address this issue in an effective way, recycling CDW in a most appropriate way has become a global concern in recent years. To this end, this study focused on the utilization of CDW-based materials such as hollow brick (HB), red clay brick (RCB), roof tile (RT), glass (G) and concrete (C) in the production of geopolymer mortars. These materials were first collected from an urban transformation area and then subjected to an identical two-step crushing-milling procedure to provide sufficient fineness for geopolymerization. To investigate the influence of blast furnace slag (S) addition to the CDW-based mixtures, 20% S substituted mixture designs were also made. Fine recycled concrete aggregates (FRCA) obtained from crushing and sieving of the waste concrete were used as the aggregate. A series of mixtures were designed using different proportions of three distinct alkali activators such as sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and calcium hydroxide (Ca[OH]2). To improve their applicability, the mixtures were left to cure at room temperature rather than the heat curing which is frequently applied in the literature. After 28 days of ambient curing, the 100% CDW-based geopolymer mortar activated with three different activators reached a compressive strength of 31.6 MPa, whereas the 20% S substituted geopolymer mortar achieved a compressive strength of 51.9 MPa. While the geopolymer mortars activated with only NaOH exhibited poor performance, it was found that the use of Na2SiO3 and Ca(OH)2 improved the compressive strength. Main geopolymerization products were related to NASH, CASH, and C(N)ASH gel formations. Our results demonstrated that mixed CDW-based materials can be employed in the manufacturing geopolymers, making them potential alternatives to Portland cement-based systems by being eco-friendly, energy-efficient, and comparable in compressive strength. / This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 894100.

This paper presents results on experimental research for concrete produced using recycled coarse aggregates (RCA). Five types of coarse aggregates were used in this study, four of which were RCA. The main purpose of this research was to examine how different types and properties of coarse aggregate affected compressive strength, modulus of elasticity, and shrinkage in concrete when natural coarse aggregates were replaced with RCA. Concrete batches were made with water-cement (w/c) ratios of 0.30, 0.45, and 0.60, and substitution percentages ranged from 0% to 100% of natural aggregate with RCA. Test results clearly show that compressive strength, modulus of elasticity, and shrinkage greatly depend on the quality and type of coarse aggregate used. In addition to testing of hardened concrete, predictive models for elasticity and ultimate shrinkage were developed to formulate and reinforce proposed conclusions about the properties and performance for the different RCA.

Yes / Demolition and reconstruction of degrading structures alongside with the repetitive repair, maintenance, and renovation applications create significant amounts of construction and demolition waste (CDW), which needs proper tackling. The main emphasis of this study has therefore been placed on the development of concrete mixtures with components (i.e., aggregates and binder) coming entirely from CDW. As the binding phase, powdered CDW-based masonry units, concrete and glass were used collectively as precursors to obtain geopolymer binders, which were then incorporated with CDW-based fine and coarse concrete aggregates. Together with the entirely CDW-based concretes, designs were also proposed for companion mixtures with mainstream precursors (e.g., fly ash and slag) occupying some part of the CDW-based precursor combination. Sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and calcium hydroxide (Ca[OH]2) were used at various concentrations and combinations as the alkaline activators. Several factors that have impact on the compressive strength results of concrete mixtures, such as mainstream precursor replacement rate, al-kaline molar concentrations, aggregate-to-binder ratios and curing conditions, were considered and these were also backed by the micro-structural analyses. Our results showed that through proper optimiza-tion of the design factors, it is possible to manufacture concrete mix-tures entirely out of CDW with compressive strength results able to reach up to 40 MPa under ambient curing. Current research is believed to be very likely to promote more innovative and up-to-date techniques to upcycle CDW, which are mostly downcycled through basic practices of road base/sub-base filling, encouraging further research and increas-ing the awareness in CDW issue. / The full-text of this paper will be released for public view at the end of the publisher embargo on 1 Jul 2024.

No / The main aim of this study is to investigate the effects of nano-SiO2 (NS), nano-Al2O3 (NA), nano-TiO2 (NT) and nano-Fe2O3 (NF) particles in single, binary, ternary, and quaternary combinations on compressive, splitting tensile, and flexural strengths of concrete. The residual compressive strength of control and nano-added concretes are also determined at 300, 500, and 800 °C elevated temperatures. Furthermore, X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses have been conducted to examine the chemical composition and microstructure of concrete samples. The main parameters investigated were the amount and various combinations of NS, NA, NT and NF, producing thirty-one concrete batches, one control and thirty NS, NA, NT and NF added concrete mixes. The total nanoparticle amounts in the concrete mixes of 0.5%, 1%, and 1.5% by weight of cement were studied. A total of 558 concrete specimens with nanoparticles were tested at 28 days to determine compressive, splitting tensile, flexural, and residual compressive strength of concretes at ambient and elevated temperatures. It can be clearly concluded that NS and NA particles are more effective than NT and NF particles in improving the mechanical properties of concrete. The largest increase in compressive, splitting tensile, and flexural strength was obtained for 1.5% of NS and NA hybrid combination as 13.95%, 18.55%, and 21.88%, respectively. Furthermore, the residual compressive strength of single and hybrid nano-added concrete specimens significantly reduced, especially at 800 °C. Although the largest decrease in residual compressive strength of 57.65% was recorded for control concrete, the lowest reduction of 41.59% was observed for concrete with 1.5% of NS and NA hybrid combination at 800 °C.

Yes / Geopolymers are mostly produced with main-stream precursors such as fly ash and slag. These precursors are successfully used and competitively demanded by the cement industry. Development of geopolymers from alternative precursors is appealing. The main aim of this work is the development of geopolymers with construction and demolition waste-based precursors including masonry units (red clay brick, roof tile, hollow brick) and glass. Different curing temperatures (50, 65, 75, 85, 95, 105, 115, 125 oC), curing periods (24, 48, 72 h), and Na concentrations (10, 12, 15%) of alkaline activator (NaOH) were employed. Compressive strength testing and microstructural investigations were performed including X-ray diffraction, thermogravimetry and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Results showed that depending on the type of precursor (hollow brick), curing temperature/period (115 oC/24 h) and concentration of alkaline activator (12%), it is possible to obtain compressive strength results more than 45 MPa. Hollow brick is the most successful precursor resulting in higher compressive strength results thanks to a more compact microstructure. The strength performance of red clay brick and roof tile is similar. The compressive strength results of geopolymers with glass precursor are lower, most probably due to significantly coarser particles of glass used. The main reaction products of red clay brick-, roof tile- and hollow brick-based geopolymers are sodium aluminosilicate hydrate (N-A-S-H) gels with zeolite-like structures while they are sodium silicate gels in the case of glass-based geopolymers. Our findings showed that CDW-based materials can be used successfully in producing geopolymers. Current research is believed to help raise awareness in novel routes for the effective utilization of such wastes which are realistically troublesome and attract further research on the utilization of CDW-based materials in geopolymer production. / The authors gratefully acknowledge the financial assistance of the Scientific and Technical Research Council (TUBITAK) of Turkey and British Council provided under projects: 117M447 and 218M102.

No / It is known that lime was added to historic Roman cement render mortars. The focus of this work is the influence of the combination of NHL5 and CL90 with Roman cement in mortars for restoration; however, the results indicate a wider potential for render applications in general. It is shown that simply adding lime to Roman cement does not retard its hydration and yields mortars where the binding action of the cement is compromised by the mixing process. If the cement is retarded by means of a pre-hydration process, hybrid mortars can be produced with improved workability and workable life as well as permitting the fine control of strength and moisture transport.

Yes / Degrading infrastructure and applications of structural demolition create tremendous amounts of construction and demolition waste (CDW) all around the world. To address this issue in an effective way, recycling CDW in a most appropriate way has become a global concern in recent years. To this end, this study focused on the valorization of CDW-based materials such as tile, bricks, glass, and concrete in the development of geopolymer mortars. CDWs were first collected from demolition zone and then subjected to crushing-milling operations. To investigate the influence of slag (S) addition to the mixtures, 20% S substituted mixture designs were also made. Fine recycled concrete aggregates (FRCA) obtained from crushing and sieving of the waste concrete were used as the aggregate. A series of mixtures were designed using different proportions of three distinct alkali activators such as sodium hydroxide (NaOH), sodium silicate (Na2SiO3), and calcium hydroxide (CH; Ca(OH)2). To improve their applicability, the mixtures were left to cure at room temperature rather than the heat curing which is frequently applied in the literature. After 28 days ambient curing, the 100% CDW-based geopolymer mortar activated with three different activators reached a compressive strength of 31.6 MPa, whereas the 20% S substituted geopolymer mortar showed a 51.9 MPa compressive strength. While the geopolymer mortars activated with only NaOH exhibited poor performance, it was found that the use of Na2SiO3 and CH improved the mechanical performance. Main geopolymerization products were related to NASH (Sodium alumino-silicate hydrate), CASH (Calcium alumino-silicate hydrate), and C(N)ASH gel formations. Results demonstrated that mixed CDWs can be employed in the manufacturing geopolymers, making them potential alternatives to Portland cement (PC)-based systems by being eco-friendly, energy-efficient, and comparable in compressive strength. / This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 894100.

The objective of this laboratory research was to investigate the effects of a higher water-cementitious materials ratio on selected properties of concrete mixtures comprising natural pozzolans. The scope of work included testing of six concrete mixtures, including one for each of three natural pozzolans at two water-cementitious materials ratios of 0.44 and 0.48 and one concrete mixture without pozzolan at a water-cementitious materials ratio of 0.44, which was treated as a baseline in this research. The stiffness and strength of each concrete mixture were measured at 1, 3, and 7 days using concrete specimens that were cast immediately after mixing. Additionally, to investigate the effects of delayed casting time, slump was measured at 0, 15, 30, 45, and 60 minutes after mixing, and cylinders were cast at 15, 30, 45, and 60 minutes for stiffness and strength testing at 7 days. Two mixtures comprising natural pozzolan experienced greater slump loss, on average, than the baseline mixture, while all of the other mixtures experienced less slump loss, on average, than the baseline mixture. Overall, the slump losses of mixtures comprising natural pozzolans were 121% and 71% of that of the baseline mixture for water-cementitious materials ratios of 0.44 and 0.48, respectively. Modulus of elasticity values ranged from 1692 ksi to 1794 ksi for mixtures comprising natural pozzolan compared to a value of 1791 ksi for the baseline mixture at 7 days. Compressive strength values ranged from 4087 psi to 4152 psi for mixtures comprising natural pozzolan compared to a value of 4795 psi for the baseline mixture at 7 days. The modulus of elasticity values of mixtures comprising pozzolans were 97% and 94% of that of the baseline mixture for water-cementitious materials ratios of 0.44 and 0.48, respectively, at 7 days. Similarly, the compressive strength values of mixtures comprising pozzolans were 86% and 71% of that of the baseline mixture for water-cementitious materials ratios of 0.44 and 0.48, respectively, at 7 days. Comparisons of the 7-day stiffness and strength results associated with casting delay time for mixtures comprising natural pozzolan with those of the baseline mixture indicate that all mixtures comprising natural pozzolan exhibited lower modulus of elasticity and compressive strength than the baseline mixture. Overall, the modulus of elasticity values of mixtures comprising natural pozzolans were 94% and 84% of that of the baseline mixture for water-cementitious materials ratios of 0.44 and 0.48, respectively, for a casting delay time of an hour. Similarly, the compressive strength values of mixtures comprising natural pozzolans were 85% and 64% of that of the baseline mixture for water-cementitious materials ratios of 0.44 and 0.48, respectively, for a casting delay time of an hour.

Masonry is a layered composite consisting of mortar and the masonry unit. Perfect bond between the masonry unit and the mortar is essential for the masonry to perform as one single entity in order to resist the stresses due to various loading conditions. Nature of stresses developed in the masonry unit and the mortar and the failure pattern of masonry subjected to compression greatly depends upon the relative stiffness of the masonry unit and the mortar. The thesis is focused on (a) some issues pertaining to masonry unit – mortar bond strength and its influence on masonry compressive strength, and (b) developing a finite element (FE) model to predict the compressive strength of masonry. Importance of masonry bond strength and masonry behaviour is highlighted in chapter 1. Characteristics of masonry units and mortars used in the investigations are presented in Chapter 2. Two types of soil-cement blocks with widely varying strength and elastic properties and cement-lime mortars of two different proportions were used in the investigations. Results of stress-strain relationships and other characteristics were determined for the blocks as well as for mortars. Block-mortar combinations were selected to have block modulus to mortar modulus ratio of <1.0, ~1.0 and >1.0. Different artificial methods of enhancing the shear bond strength of masonry couplets have been discussed in chapter 3. Shear bond strength of the masonry couplets was determined through a modified direct shear box test apparatus. Without altering the block and mortar properties, bond strength values for three block-mortar combinations were generated through experiments. Effect of pre-compression on shear bond strength has also been examined for certain block-mortar combinations. Considering five different bond strength values and three block-mortar combinations, compressive strength and stress-strain characteristics of masonry was obtained through the tests on masonry prisms. A detailed discussion on influence of shear bond strength on masonry compressive strength is presented. Major conclusions of the investigation are: (a) without altering the block and mortar characteristics shear bond strength can be enhanced considerably through the manipulation of surface texture and surface coatings, (b) masonry compressive strength increases linearly as the shear bond strength increases only for the combination of masonry unit modulus less than that of mortar modulus, (c) masonry compressive strength is not sensitive to bond strength variation when the modulus of masonry unit is larger than that of the mortar. Chapter 4 is dedicated to the development of a 3D FE model to predict the masonry compressive strength. Literature review of empirical methods/formulae and some failure theories developed to predict masonry strength are presented. Existing FE models for masonry dealing with both macro and micro modelling approaches are reviewed. The proposed FE model considers (a) 3D non-linear analysis combined with a failure theory, (b) uses multi-linear stress-strain relationships to model the non-linear stress-strain behaviour of masonry materials, (c) adopting Willam-Warnke’s five parameter failure theory developed for modelling the tri-axial behaviour of concrete, and (d) application of orthotropic constitutive equations based on smeared crack approach. The predicted values of masonry compressive strength are compared with experimental values as well as those predicted from other failure theories. The thesis ends with a summary of conclusions in chapter 5.

Characterization of rock masses and evaluation of their mechanical properties are important and challenging tasks in rock mechanics and rock engineering. Since in many cases rock quality designation (RQD) is the only rock mass classification index available, this paper outlines the key aspects on determination of RQD and evaluates the empirical methods based on RQD for determining the deformation modulus and unconfined compressive strength of rock masses. First, various methods for determining RQD are presented and the effects of different factors on determination of RQD are highlighted. Then, the empirical methods based on RQD for determining the deformation modulus and unconfined compressive strength of rock masses are briefly reviewed. Finally, the empirical methods based on RQD are used to determine the deformation modulus and unconfined compressive strength of rock masses at five different sites including 13 cases, and the results are compared with those obtained by other empirical methods based on rock mass classification indices such as rock mass rating (RMR), Q-system (Q) and geological strength index (GSI). It is shown that the empirical methods based on RQD tend to give deformation modulus values close to the lower bound (conservative) and unconfined compressive strength values in the middle of the corresponding values from different empirical methods based on RMR, Q and GSI. The empirical methods based on RQD provide a convenient way for estimating the mechanical properties of rock masses but, whenever possible, they should be used together with other empirical methods based on RMR, Q and GSI. (C) 2016 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V.