The earth-based construction with unique advantages of wide source of raw material, low energy consumption and carbon emission has attracted growing attention recently. This study employs a ...cement-based high-efficiency stabilizer and fly ash to improve the mechanical properties of earth-based construction. And the influences of fly ash on compressive strength and key variables for strength development are studied by measuring the mechanical and physical properties. Total stabilizer content (CT) which changes slightly with curing time and the calculation method of CT values are put forward based on the pozzolanic and dispersing effects of fly ash in stabilized earth. An integrated parameter taking into account multiple variables, such as stabilizer and fly ash contents, curing time and physical indexes, is defined as the ratio of void ratio to total stabilizer content (et/CT), and the relationship of compressive strength to et/CT is analyzed by exponential and power functions. The after-curing physical indexes are dependent upon the initial ones, total stabilizer content and curing age. Subsequently, the calculation formulae for physical indexes are proposed through the multiple linear regression and power regression. Finally, the strength-calculation model with a deviation between calculated values and measured results of lower than 10% is developed to guide the design of earth-based construction admixed with the high-efficiency stabilizer and fly ash. Embodied environmental impact evaluation indicates that the combination use of stabilizer and fly ash is a novel low-CO2 emission method for preparing cleaner earth-based construction.
•Higher calcination temperature reduced the dissolved degree of Al in sludge ash.•S600 ash promoted the formation of Al-bearing products but inhibited the C3S hydration significantly.•The reaction of ...S800 ash with cement contributed to more hydration heat and hydration products.
Sewage sludge ash has potential to be used as supplementary cementitious material in the production of building materials. The chemical effect of sewage sludge ash on early-age hydration of cement was investigated in this study. Two types of sludge ash calcined at 600 °C (S600) and 800 °C (S800) were blended with cement for analysis of hydration heat evolution, solid phase assemblage and aqueous composition. The aluminate dissolution of S600 ash promoted the formation of ettringite and consumption of gypsum, resulting in a high initial hydration heat. However, high concentrations of Al and Si caused by continuous dissolution of aluminate and silicate in S600 ash inhibited significantly the C3S dissolution. Interestingly, S800 ash had slight effect on early cement hydration since higher calcination temperature decreased the activity of aluminate. As compared with the reference, cumulative hydration heat of blended paste with 30% S800 ash at 7 days was increased by 18.72% indicating the occurrence of reaction between sludge ash and cement. Further study is recommended to focus on the long-term performance of cement-based materials blended with sludge ash.
•Using the SVM-PSO algorithm to predict the splitting tensile strength.•An effective classification method for the bubble defect area of the bonding interface.•Every training sample set or every test ...sample set has a 14-dimensional feature vector.
The bonding performance of the interface between two concrete layers is of great importance for China Rail Track System III (CRTS III) slab ballastless track structure. While the bonding performance is close to the distribution and amounts of defects such as the bubble or the void on the bonding interface. In this paper, combining the Support Vector Machine (SVM) with the Particle Swarm Optimization (PSO) algorithm, named SVM-PSO algorithm is used to predict the splitting tensile strength of the bonding interface based on the distribution of defects. And the influence of different parameters in the SVM-PSO algorithm on the prediction ability is discussed. Results indicate that the relative error between the average strength value of every 100 predictions and the experimental strength value is less than 5%. The achievements will provide an effective method for predicting the splitting tensile strength of the bonding interface between two concrete layers like CRTS III slab ballastless track structure in practice.
Disposal of massive scrap tires in an eco-friendly way has become a worldwide concern due to the booming automobile industry. The introduction of waste tire rubber particles into concrete as an ...alternative aggregate provides a promising way to solve the problem. It is noteworthy that the substitute of natural aggregates with rubber particles can mitigate environmental destruction and resource consumption caused by mining activities of natural aggregates. In this study, a series of experiments were conducted to evaluate both fresh and hardened properties of self-compacting concrete (SCC) with recycled tire rubber aggregate (RA), aiming at providing fundamental insight of its performance for the potential large-scale applications. Results show that the addition of RA leads to a slight decline in workability and an increase in air content of fresh SCC. Increasing RA content results in the improvement of the damping ratio, fracture energy and ductility index while a loss of compressive strength and dynamic modulus. SCC with RA also presents high strain rate sensitivity and toughness index under impact load, indicating improved impact resistance. In addition, use of RA enables SCC to achieve low water absorption and high resistance to chloride ion penetration. From the above, this study provides a comprehensive investigation of the clean and effective utilization of recycled tire rubber in concrete.
•The properties of SCC with rubber aggregate (RA) were systematically studied.•Increasing RA content or decreasing RA size reduces the workability of SCC.•The energy absorption and permeability properties of SCC are improved by RA.
The impulse response method, as a mechanical impedance analysis method with high-impact energy, can provide a rapid assessment of structural integrity. For this reason, the impulse response method is ...applied to subway slab ballastless tracks, and the theory behind this method, as well as the applicability of detecting the voids within the self-compacting concrete (SCC) filling layer, are deeply studied. The theoretical derivation of the mobility function of subway slab ballastless track under impact load is performed. The finite element model is established and the propagation of elastic waves in the process of impulse response method is simulated. The study also investigates the sensitivity of various characteristic parameters and the frequency analysis range to void identification in the SCC filling layer. Furthermore, the characteristic parameters for defect identification in the SCC filling layer are constructed and subsequently validated through a full-scale test. The results reveal that the impulse response method is capable of generating elastic waves with higher energy and longer wavelengths within the structure. This characteristic is advantageous for the detection of concealed defects in the multi-layer structure. The mobility spectrum of subway slab ballastless track exhibits multi-frequency peak characteristics, and the calculated cut-off frequency of the peak-mean mobility ratio should be extended to more than 1600 Hz. Among the three characteristic parameters of peak mobility, dynamic stiffness, and peak-mean mobility ratio, the peak-mean mobility ratio has the advantage of accurately identifying the void position and providing a more precise range.
•The propagation of elastic waves was simulated.•Characteristic parameters were reconstructed.•Verified through full-scale tests with preset defects.
Generally, tunnel waste is stacked in the slag field nearby for landfilling, which is harmful to sustainable development. The broken rocks and rock powder among the tunnel waste can be recycled to ...produce machine-made sand, producing many by-products calling rock powder. Based on the practical project, three types of waste basalt powder (BP), from tunnel excavation waste and by-products (rock powder) of machine-made sand producing from tunnel excavation waste in Sichuan-Tibet railway construction sites, was used to prepare an eco-friendly UHPC. The BP is used to replace the cement and is included in the design UHPC based on Modified Andreasen &Andersen particle packing model (MAA). Moreover, the chemical and physical behaviors and ecological evaluation of the designed UHPC and UHPC pasted were discussed. The results showed that when BP (Specific surface area 4.6582 m2/g) replaces up to 15%, the highest compressive strength of designed UHPC (220 MPa) was obtained. Compared with quartz powder, the pozzolanic activity of BP was generally low and increased with the increase of reaction temperature. However, the presence of BP and its fineness in UHPC pastes increased the values of the total autogenous shrinkage and decreased the total heat release at an early age of designed UHPC pastes, this effect is more pronounced with temperature increasing. Based on a quartering method with embodied carbon dioxide emissions and the compressive strength, UHPC with waste BP reduced embodied carbon dioxide and possessed higher compressive strength and lower environmental impact than the control samples of UHPC.
•The 28-day compressive strength of one-part geopolymer mortar can achieve over 50 MPa.•Early-term reaction is very sharp, leading to the high drying shrinkage which is related to the precursor ...component.•Gelatinous phases with the low degree of crystallinity are the main reaction products in one-part geopolymer.
One-part geopolymers are environmental-friendly construction materials and more convenient for operating in situ in comparison to conventional two-part geopolymers. A special type of fly ash (FASB) was confirmed as a novel material for preparing one-part geopolymer. This research systematically studied the properties by investigating fresh performance, strength development, sulfate resistance, acid resistance and drying shrinkage of Na2SiO3-anhydrous activated one-part geopolymer mortars with both FASB and ground granulated blast furnace slag (GGBS). The results indicate that the presence of FASB improves the workability, volume stability and sulfate and acid resistance in varying degrees, even though the replacement of GGBS by FASB decreases the compressive strength. SEM imaging detects that the addition of FASB makes the microstructure of one-part geopolymer more homogeneous. The hydration kinetics of FASB-GGBS-based one-part geopolymer is similar to that of conventional two-part geopolymer, and the initial heat release rate, induction duration and value and arrival time of the second peak are dependent upon the proportion of FASB and GGBS. Gelatinous minerals are the main reaction products in one-part non-Portland cement.
•Green UHPC based on optimization of the physical and chemical effects of binders is proposed.•Nanomaterials and chemical activator proven to improve the properties of green UHPC.•The designed green ...UHPC shows a better performance and environmental impact.
The development of Green Ultra-High Performance Concrete (GUHPC) has become a hotspot of concern in the construction industry. GUHPC with very low cement content can be prepared based on the combined optimization of the physical and chemical effects of the binder materials. On this basis, this paper proposes to prepare a new GUHPC by further enhancing chemical effects of the binder materials through the addition of nanomaterials and chemical activator. Series of experiments are designed to investigate the mechanical properties and environmental impact in respect to embodied CO2-emissions of GUHPC. The hydration characteristics and the pore structure of GUHPC are evaluated by employing thermogravimetry analysis and mercury intrusion porosimetry. The results show that GUHPC with good mechanical performance and very low environmental impact can be prepared with very low cement content (no more than 370 kg/m3). The high initial packing density of GUHPC can be achieved by application of multi-scale particles system, especially in the presence of nano-scale particles. Chemical activator can effectively improve the reactivity of binder materials and promote the hydration of GUHPC. The GUHPC has lower porosity and finer pore size than UHPC.
•Investigate two-dimensional digital characterization of crushed stone aggregates in the SCC.•Two-dimensional images in three directions of each aggregate.•Comparison of the sphericity, the flatness, ...the circularity and fractal dimension.
Through the actual situation of on-site construction and building, it could be found that the filling quality of the SCC filling layer had a large correlation with the apparent morphology of crushed stone aggregates. This paper investigated the two-dimensional digital characterization of crushed stone aggregates in the SCC filling layer of the CRTS III slab ballastless track through field experiments and compared them with pebble aggregates from three perspectives. Two-dimensional feature data of crushed stone and pebble aggregates in the top view, front view, and left view were obtained using the 3D scanning equipment. The sphericity (or flatness, or circularity) of both crushed stone and pebble aggregates did not directly reflect a uniform pattern of variation in the three views. Pebble aggregates exhibited higher concentration of the sphericity (or flatness, or circularity), while crushed stone aggregates showed more dispersed values. Furthermore, the fractal dimension of crushed stone aggregates was greater than that of pebble aggregates in the corresponding view, with the fractal dimension of crushed stone aggregates tending towards larger values. Regarding the characteristic indices of crushed stone and pebble aggregates, including the sphericity, flatness, and circularity, significant differences were observed between the different characteristic indices. This research provided effective suggestions for the preparation of the SCC with excellent flow characteristics at the construction site.
To investigate the reasons for the mitigation of drying shrinkage but earlier cracking in limestone powder cement paste, various admixtures such as fly ash, metakaolin, super-absorbent polymer, and ...expansion agent were selected for the above-mentioned experiments. The effects of mixing two admixtures on the drying shrinkage deformation and crack resistance performance of the limestone powder-cement paste was studied. Additionally, hydration exotherm, hydration products, microscopic morphology of samples were analyzed to understand the underlying mechanisms. Based on the hydration process, the addition of fly ash and metakaolin can promote the formation of carbon aluminate in the reaction system, thereby reducing the porosity. Fly ash is more beneficial for the hydration heat peak value of cement paste, effectively eliminating temperature strain. The results indicate that effects of mixing two admixtures on the improvement of drying shrinkage and crack resistance of limestone powder cement paste are much better than using a single admixture. Among them, the combination of metakaolin and expansion agent shows the best overall mitigating effect on the drying shrinkage and crack resistance of limestone powder cement paste. This compound admixtures reduces the drying shrinkage of the paste by approximately 30% and delays the cracking time of the specimens by 34.4 h.
•The utilization of limestone powder in limestone powder cement paste can be effectively enhanced by mixing two admixtures.•Using a smaller ring size for the ring test to monitor the cracking resistance of cement paste.•The application of linear fitting revealed that the moisture loss characteristics of cement paste manifest in two stages.•Analyzing the reasons for the mitigation of drying shrinkage but earlier cracking in limestone powder cement paste.
