Abstract
The article presents the results of experimental determination of the oscillation law of the proposed additional conical spring mechanism of the effective reaction. The results of ...calculation of compressive strength and spring elasticity are presented. The change in the force acting on the reaction is determined by the electrostrain method and is based on its parameters.
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•MSWIFA was used for manufacturing alkali-activated cementitious material.•Blending 10 % of MK significantly increased the compressive strength.•C-S-H was identified in AAFA, whereas ...C-(A)-S-H and ettringite was observed in AAFM.•Concentrations of heavy metal in AAFM were significantly reduced to the recommendation in Chinese standards.•AAFM reduced 64.8 % of total TEQ of PCDD/Fs in MSWIFA.
The proper treatment on hazardous municipal solid waste incineration fly ash (MSWIFA) is important. The application of alkali-activation technology to prepare alkali-activated MSWIFA (AAFA) material provides a potential not only to immobilise the heavy metals, but also to trigger its pozzolanic property in manufacturing building material. In this study, in addition to investigate the feasibility of alkaline activation technology in preparing AAFA with sodium silicate activator, the effect of metakaolin in AAFA (AAFM) was also explored to enhance its performance. The results showed that, compared to the AAFA, blending 10 % metakaolin in AAFA significantly improved both 28-day and 90-days compressive strengths, which was almost 200 % higher than that of AAFA. The compressive strength was increased with increasing the dosage of sodium silicate. The C-S-H gel was observed as the main hydration product of AAFA and AAFM. Moreover, the ettringite was observed in AAFM due to the reaction between the CaSO4 in MSWIFA and aluminate phase from metakaolin. Finally, the 28 and 210-day leaching behaviours of AAFM on Zn, Cu, Pb, Cd, Cr and Ni were successfully suppressed to less than 1 % of that originally from MSWIFA, which can meet the requirement from Chinese standards.
Geopolymers show high quasi-brittle behavior because of their ceramic-like characteristics. Recent findings have indicated that graphene can be used as an additive to improve the mechanical ...properties of composites. In this study, we report the effect of the addition of graphene nanoplatelets (GNPs) on the microstructure and mechanical properties of a fly ash based geopolymer. The GNPs are relatively homogeneously distributed in the matrix of all composites. However, overlapping and agglomerate formation of GNPs was detected by FESEM. The results showed that the compressive and flexural strength of the geopolymer improved by 1.44 and 2.16 times, respectively, when adding 1% GNPs. The introduction of a GNP filler, even at low filler weight fractions, increased the toughness, stress and strain at the first crack and rigidity. Moreover, the wettability decreased with an increase in GNP content.
Sodium silicate modified polyurethane (SS/PU) and polyurethane (PU) have become the most widely used grouting materials at present, but their differences in mechanical properties and fracture ...characteristics remain unclear. In this study, uniaxial compression, digital image correlation (DIC), split Hopkinson pressure bar (SHPB), and scanning electron microscopy were used to compare the dynamic and static mechanical properties and fracture characteristics of the two materials at different aging times. In terms of static mechanics, the stress-strain curve evolution, compression strength characteristics, and crack evolution fracture of SS/PU and PU were compared and analyzed. In dynamic mechanics, the impact compression stress-strain curve, peak strength, strength evolution characteristics, and micro-damage fracture characteristics of the materials were explored. Based on static compression measurements, both materials belong to viscoelastic bodies, with SS/PU being more rigid and PU being more elastic. SS/PU exhibits higher early strength (6 h, 36.9 MPa), while PU shows higher later strength (36 h, 48.9 MPa). Cracks appear instantaneously before or after the peak strength in both materials, with vertical cleavage fracture predominating. Under dynamic impact compression, both materials exhibit an increase with increasing impact velocity, showing a significant strain rate strengthening effect. At different aging times (6 h, 12 h, 24 h, 36 h), the dynamic compression strength of PU is greater than that of SS/PU. The fracture of SS/PU mainly involved continuous fracture, while the fracture of PU mainly involved polymer tearing. In general, when grouting reinforcement projects require materials with higher early strength and better rigidity, SS/PU is more suitable. If the area to be reinforced is in a dynamic impact environment and requires higher final strength, PU is preferable.
•Mechanical properties and fracture characteristics between WG/PU and PU materials are compared.•Both WG/PU and PU materials exhibit high early compressive strength (>30 MPa at 6 hours).•The dynamic compression strength of PU is greater than that of WG/PU under different aging times.•This work provides a basis for grouting reinforcement engineering.
•Mechanical properties of coral concrete under quasi-static and dynamic compressions are investigated.•Coral concrete exhibits high-early strength and more brittle characteristics.•The compressive ...strength and failure pattern are sensitive to strain rate.•Energy dissipation and fractal dimension are calculated and found to be rate-dependent.•Differences of failure pattern and mechanism between coral and conventional concrete are analyzed.
The uniaxial compressive behavior of coral aggregate concrete was experimentally investigated under quasi-static to dynamic loading rates. Quasi-static compression tests of coral concrete at different curing ages were performed at a constant strain rate of 10−5 s−1 using an electro-hydraulic servo-controlled test machine. Dynamic impact loading tests were conducted at stain rates from 101.48 s−1 to 102.16 s−1 utilizing a 100-mm-diameter split Hopkinson pressure bar (SHPB) system. The strain rate effects on the mechanical properties of coral concrete were assessed in terms of the uniaxial compressive strength, energy dissipation, fractal dimension and failure pattern. The coral concrete exhibits high-early strength and the post-peak stress-strain curves behave in a more brittle manner than conventional concrete. A more remarkable rate-dependence in the compressive strength of coral concrete than other cement-based composites was observed as the dynamic increase factor (DIF) increased from 1.73 to 2.56 with the strain rate increasing from 30.12 s−1 to 143.32 s−1. Different from the failure pattern of conventional concrete, the fracture plane of coral concrete directly penetrated through the coral shingles rather than cracking in the interface between the cement mortar and the coarse aggregate under both quasi-static and dynamic loadings, ascribing to the low strength of coral aggregates and the high intensity of bonding interface. The ratio of the absorbed energy to incident energy is between 0.3–0.5 and tends to decrease with an increase in strain rate. A higher loading rate may lead to more energy absorption consumed by generating more fracture planes and smaller fragments, which is in consistent with a higher value of fractal dimension. The fractal dimension in the range of 2.027–2.302 for coral concrete was also found to be proportional to the logarithm of the loading strain rate.
This research is an investigation of the feasibility of utilizing phosphogypsum (PG) and phosphate tailings (PTS) for cemented paste backfill. Some experiments were conducted with various ...combinations of PTS and PG as aggregates, along with slags and/or Portland cement as binders and CaO as an additive. The influence of the PG's ageing time on the consolidation of backfill was also explored. The unconfined compressive strength (UCS), the generated gases and the scanning electron microscope (SEM) were all tested and used in the analysis of backfill characteristics. The results show that (i) the highest UCS of backfill prepared by PG and PTS after curing for either 7 days or 28 days is still less than 1.0 MPa, with a large amount of CO2 and SO2 generated; (ii) the slags can improve the UCS by a factor of three, but not without a vast generation of CO2, SO2, and H2S. However, the gases were not produced when CaO was added, but the UCS decreases suddenly to 0.2 or 0.4 MPa after curing for 7 days or 28 days, respectively; (iii) the UCS of backfill increases linearly with increasing cement content. When the CaO was added at 2%, the UCS reached 3.36 MPa after curing for 7 days and 4.44 MPa after curing for 28 days, and no gases were generated; (iv) the influence of the PG's ageing time on the UCS is negligible after 4 days of aging. Based on these results, it was concluded that PG and PTS can be utilized as backfill materials when Portland cement is used as a binder and CaO is used as an additive.
•The phosphogypsum (PG) and phosphate tailings (PTS) are not suitable for cemented paste backfill (CPB) by themselves for the low strength and vast generated CO2 and SO2.•The slags are not a good binder for the PG and PTS even after adding CaO.•The Portland cement is a good binder with the addition of CaO at 2 wt. %.•The PG's ageing time has a significant influence on the consolidation characteristics.
The influences of fly ash and metakaolin added as substitutions (by up to 50 wt%) of magnesium potassium phosphate cement (MKPC) on the microstructures and compressive strengths of the MKPC pastes ...were investigated. The results indicate that the aluminosilicate fractions of both fly ash and metakaolin are involved in the acid-base reaction of MKPC system, leading to a preferential formation of irregular crystalline struvite-K incorporated with Al and Si elements and/or amorphous aluminosilicate phosphate products. Metakaolin is more reactive than fly ash in the MKPC system. For the same addition dosage, the MKPC pastes containing metakaolin exhibit higher compressive strengths than the pastes containing fly ash. This is attributed to the formation of more highly reinforced microstructures and denser interfaces between the metakaolin particle and hydration products (e.g. struvite-K) in the MKPC paste containing metakaolin. Addition of 30 wt% metakaolin increases the compressive strengths of MKPC pastes at all test ages.
