Durability design and performance of self-consolidating lightweight concrete

In terms of the durability, the reduction in cement paste is crucial to both volume stability and long-term performance of concrete. The objective of this paper is to compare the performance of lightweight concrete under different w/cm ratio and different cement paste content. The slump and slump flow spread of fresh self-consolidating lightweight concrete (SCLWC) are designed to be within 230–270 and 550–650 mm, respectively. The test results indicate that the 91-day compressive strength of SCLWC is up to 56 MPa when cement content is 386 kg/m³ and water content is 150 kg/m³. If enough cement paste is used, then the less the paste amount and the denser the packing of aggregate, the higher the strength efficiency of cement and the electric resistance, and the lower the chloride ion penetrability capacity of SCLWC.     

Development of sustainable engineered stone cladding for toughness,durability, and energy conservation

This study aims to investigate the techniques of manufacturing an improved engineered stone for better toughness, ductility, durability, and thermal resistance. The new artificial stone consists of two layers. The face layer is made strong, durable, colored, and smooth/or textured for natural look, while the back layer is light, high impact resistance, and low heat conductivity for better insulation and energy cost. The back layer utilizes recycled crumb rubber, which provides a combined solution for energy saving and environmental concerns. It reduces the material unit weight, enhances ductility and toughness, and improves thermal resistance. The stone’s properties such as compressive strength, thermal conductivity, durability, impact resistance and water absorption were experimentally measured and compared with natural stone specimens.     

Autoclaved brick from low-silicon tailings

The load-bearing brick is made from low-silicon tailings by pressing and autoclaving process, in the presence of alkali-activated slag/fly ash cementing material (AAFSC). Tailings accounts for 83% of the total mass of the brick. The compressive strength of the brick is up to 16.1 MPa, bending strength 3.8 MPa, and with low drying shrinkage and good freeze–thaw resistance. Some factors influencing the mechanical strength of the brick including forming pressure, forming water content and curing regime, are investigated. The hydration products, freeze–thaw durability and anti-carbonation characteristics of the products are discussed.     

Comparison of UV/H(2)O(2) and UV/TiO(2) for the degradation of metaldehyde: Kinetics and the impact of background organics

The kinetics of photodegradation of the pesticide metaldehyde by UV/H₂O₂ and UV/TiO₂ in laboratory grade water and a natural surface water were studied. Experiments were carried out in a bench scale collimated beam device using UVC radiation. Metaldehyde was efficiently degraded by both processes in laboratory grade water at identical rates of degradation (0.0070 and 0.0067 cm² mJ⁻¹ for UV/TiO₂ and UV/H₂O₂ respectively) when optimised doses were used. The ratio between oxidant and metaldehyde was significantly higher for H₂O₂ due to its low photon absorption efficiency at 254 nm. However, the presence of background organic compounds in natural water severely affected the rate of degradation, and whilst the pseudo first-order rate constant of degradation by UV/H₂O₂ was slowed down (0.0020 cm² mJ⁻¹), the degradation was completely inhibited for the UV/TiO₂ process (k′ = 0.00007 cm² mJ⁻¹) due to the blockage of active sites on TiO₂ surface by the background organic material.     

Development of alpha plaster from phosphogypsum for cementitious binders

Efforts have been made to make high strength alpha plaster from phosphogypsum, a by-product of phosphoric acid industry. Phosphogypsum was autoclaved in slurry form (phosphogypsum 50% + water 50%, by wt.) in the laboratory at different steam pressures for different durations in presence of chemical admixtures. It was found that with small quantity of chemical admixture (sodium succinate/potassium citrate/sodium sulphate), alpha plaster of high strength can be produced. The optimum pressure and duration of autoclaving was found to be as 35 psi and 2.0 h, respectively. The alpha plaster was examined for making cementitious binders by admixing hydrated lime, fly ash, granulated blast furnace slag, marble dust and chemical additives with alpha plaster. Data showed that cementitious binder of compressive strength of 22.0 and 30 MPa (at 28 days of curing at 40° and 50 °C) and low water absorption was produced. DTA and SEM studies of the binder showed formation of CSH, ettringite and C₄AH₁₃ as main cementitious products to give strength.     

Effect of temperature and pressure on the thermal conductivity of sandstone

Effective thermal conductivity (ETC) of dry sandstone was measured over a temperature range from 275 to 523 K and at pressures up to 400 MPa with a guarded parallel-plate apparatus. The estimated uncertainty of the ETC measurements is 2%. The porosity of the sample was 13%. A rapid increase of ETC was found for dry sandstone at low pressures between 0.1 and 100 MPa along various isotherms. At high-pressure range (P>100 MPa) a weak linear dependence of the ETC with pressure was observed. The pressure effect is negligibly small after first 80–100 MPa where bridging of microcracks or improvement of grain contacts takes place. We interpreted the measured ETC data using a various theoretical and semi-empirical models in order to check their accuracy and predictive capability. The effect of structure (size, shape, and distribution of the pores), porosity, and mineralogical composition on temperature and pressure dependences of the ETC of sandstone was discussed. To estimate the effect of temperature and pressure on the ETC of sandstone the pressure, β_P, and temperature, β_T, coefficients of ETC were calculated from the measured values of ETC. The measured values of the ETC were also used to calculate the values of the isothermal compressibility, χ_T, and thermal expansion coefficient, α. The equation of state of sandstone was developed using the measured ETC data.     

Study of high performance autoclaved shell-aggregate from propylene oxide sludge

This study focuses on the comprehensive utilization of propylene oxide sludge (POS). High performance propylene oxide sludge aggregate (POSA), whose main hydrated phase is tobermorite, was prepared by the hydrothermal synthesis of POS and silica materials under the condition of 180 °C saturated steam. The factors affecting the performance of the aggregate were investigated systematically by orthogonal experiments, thus aggregate with cylinder compressive strength between 6.14 and 13.52 MPa, bulk density between 882 and 1163 kg/m³, apparent density between 1515 and 1916 kg/m³, 1 h water absorption rate between 4% and 14%, 24 h water absorption rate between 11% and 19%, the mass loss of freezing and thawing between 1.63% and 3.92% was achieved. By single-factor analysis, it was shown that cylinder compressive strength and specific strength of propylene oxide sludge shell-aggregate (POSS-A) increases by 21.3% and 13.9%, respectively, in contrast to the POSA with no shell. At the same time, 1 h water absorption rate and 24 h water absorption rate decreases by 57% and 20%, respectively. The compressive strength of the concrete with POSS-A as coarse aggregate reaches 80 MPa, which is 8.1% higher than that of the crushed stone concrete. In addition, the density gets lowered by 17%. The HVEP results of analysis of the aggregate imply that heavy metals are solidified inside aggregate and the POSA thus fabricated is non-hazardous for construction use.     

Lightweight granular material from zeolite rocks with different additives

This paper presents the results of investigations related to the development of a novel low temperature technology for obtaining light porous granular materials based on zeolite rock. Using a process temperature as low as 850 °C, porous, granulated material was obtained, having a compressive strength of 3–6 MPa, a bulk density of 380–600 kg/cm³ and a water absorbtion of 3–8%. Optionally, ash microspheres or foamed vermiculite can be added in fractions of 3–5% to increase strength.     

Freeze–thaw cycle test and damage mechanics models of alkali-activated slag concrete

Alkali-activated slag concrete (ASC) was prepared by using slag and Na₂SiO₃, NaOH complex activator. Freeze–thaw resistance, microstructure, performance mechanism, inner freeze–thaw damage distribution and mechanics models of ASC were investigated by freeze–thaw cycle, SEM and EDS tests. The experimental results show that ASC has excellent freeze–thaw resistance with frost-resisting grade of F300 at lowest; hydration products of ASC are mostly C–S–H(I) with low Ca/Si, alkaline aluminosilicate and zeolite mineral, it does not have Ca(OH)₂ and transition strip, compact degree and uniformity of structure are better, and its high compressive strength (90 MPa) also makes high freeze–thaw resistance, therefore, ASC has excellent freeze–thaw durability; freeze–thaw damage mechanics models of ASC were established by using relative dynamic elasticity modulus, dynamic elasticity modulus attenuation model is superior to accumulative freeze–thaw damage model, power function model is superior to exponential function model with better precision and relativity, and the models can reflect freeze–thaw damage rule and degree accurately.     

隧道石粉取代胶凝材料对机制砂混凝土性能的影响

以石粉部分取代混凝土中的胶凝材料,研究石粉取代量为0, 10%, 15%, 20%, 25%, 30%时的机制砂混凝土性能,测试混凝土抗压强度、抗硫酸盐侵蚀、碳化深度、抗氯离子扩散系数等性能指标。结果显示,当水胶比、石粉细度固定时,混凝土性能随石粉取代量增加而降低;当石粉取代胶材量为15%、石粉细度为30%、水胶比为0.5时,28d抗压强度大于34.5MPa。     

Effects of NO2 on oxidation mechanisms of atmospheric pollutant SO2 over Baumberger sandstone

The influence of NO₂ on oxidation of atmospheric pollutant gas SO₂ has been studied through Baumberger sandstone degradation. Experiments were conducted in a set of laboratory atmospheric chambers. By exposure of stone specimens to various pollutant regimes; e.g. single and combined pollutant gases (SO₂, NO₂), the reaction products (i.e. nitrite, nitrate, sulphite and sulphate) collected from run-off solutions as well as extracted from stones were analysed. Presentation rates of pollutant gases in terms of mg/cm² s have been used to assess the interaction of SO₂ and NO₂ pollutant gases with Baumberger sandstone. For the first time, the contribution of NO₂ to SO₂ oxidation over the sample surface has been quantified (e.g. 37% in dry surface condition and 9% in wet surface condition). SO₂ oxidation over Baumberger sandstone in the presence of NO₂ produces nitrates over the surface of the sample; however, when no sandstone is present no NO₂ oxidation is produced.     

Properties of self-compacting concrete mixtures containing metakaolin and blast furnace slag

Rheological, mechanical and durability properties of self-compacting concrete (SCC) mixes produced using blended binders containing metakaolin and blast furnace slag are studied. The rheological properties of SCC mix with metakaolin are characterized by significant yield stress and relatively low viscosity, while the mix with blast furnace slag shows zero yield stress and higher viscosity. The compressive strength of SCC with metakaolin grows very fast during the initial hardening period and remains significantly higher, as compared with the mix with blast furnace slag, up to 90 days. Durability properties of the mix containing metakaolin are excellent. Water absorption coefficient and water penetration depths are very low. The freeze resistance tests show zero mass loss after 56 cycles in deicing salt solution.     

Stabilizing blended calcium sulfate materials for roadway base construction

Blended calcium sulfate (BCS), a recycled fluorogypsum waste material, has been used in Louisiana as a pavement base layer for more than a decade. Without further chemical stabilization, the major concern of using raw BCS as a pavement structural layer is its moisture resistance. It could cause both short-term construction difficulties and long-term performance problems. In order to improve the moisture susceptibility of BCS, various cementitious agents were used in the laboratory for BCS stabilization. To further verify the efficiency of BCS stabilization schemes obtained from laboratory and assess the field performance for stabilized BCS materials as well as potential cost-benefits, three pavement test sections were constructed and tested using the accelerated loading facility (ALF) device. Both laboratory and field test results indicated that a grade 120 granulated ground blast furnace slag (GGBFS) of 10 vol.% stabilized BCS material possessed a superior performance over raw BCS in terms of water resistance, durability, and good long-term performance. Field test results further demonstrated that the GGBFS stabilized BCS base outperformed both a regular crushed stone base and a fly ash stabilized BCS base by a significantly large margin.A life-cycle cost analysis proved that, besides its outstanding laboratory and field performance, using the GGBFS stabilized BCS can provide a substantial long-term savings over regular crushed stone and fly ash stabilized BCS bases in a 30-year pavement design life period.     

Mix proportion of high-strength,roller-compacted,latex-modified rapid-set concrete for rapid road repair

In this study, we optimized a blend of high-strength, roller-compacted, latex-modified rapid-set concrete (RCLMC) that can be re-opened to traffic after 4 h. To this end, we tested several variables in laboratory experiments, including hardening acceleration agents, cement type, latex addition, and CSA admixture ratios. The target compressive strength was 21 MPa after 4 h. A mixture of Type III cement to CSA admixture at 235:165 kg/m³ (400 kg/m³ total binder) and 23.5 kg/m³ latex (10% of the cement weight) achieved the target compressive strength and was the most economically efficient.     

Stress-dependence of the permeability and porosity of sandstone and shale from TCDP Hole-A

We utilize an integrated permeability and porosity measurement system to measure the stress dependent permeability and porosity of Pliocene to Pleistocene sedimentary rocks from a 2000 m borehole. Experiments were conducted by first gradually increasing the confining pressure from 3 to 120 MPa and then subsequently reducing it back to 3 MPa. The permeability of the sandstone remained within a narrow range (10^?14–10^?13 m²). The permeability of the shale was more sensitive to the effective confining pressure (varying by two to three orders of magnitude) than the sandstone, possibly due to the existence of microcracks in the shale. Meanwhile, the sandstone and shale showed a similar sensitivity of porosity to effective pressure, whereby porosity was reduced by about 10–20% when the confining pressure was increased from 3 to 120 MPa. The experimental results indicate that the fit of the models to the data points can be improved by using a power law instead of an exponential relationship. To extrapolate the permeability or porosity under larger confining pressure (e.g. 300 MPa) using a straight line in a log–log plot might induce unreasonable error, but might be adequate to predict the stress dependent permeability or porosity within the experimental stress range. Part of the permeability and porosity decrease observed during loading is irreversible during unloading.     

Preparation of load-bearing building materials from autoclaved phosphogypsum

Previous studies have been carried out on calcined phosphogypsum (PG) for making the building materials. The present study was focused on autoclaved PG and its use in making load-bearing wall bricks. Autoclaved PG was prepared from original waste PG with steam pre-treatment. The crystalline phase, morphology, and thermal characteristics of original waste PG and autoclaved PG were investigated by XRD, SEM, and SDT. Then bricks of the size of Chinese standard brick were prepared from different types of PG in the PG-fly ash–lime–sand system. Results showed that the compressive strength of bricks from autoclaved PG by lower-pressure steam of 0.12 MPa, 120 °C for 16 h was much higher. The flexural strength and compressive strength of the bricks could reach 4.0 MPa and 15.0 MPa, respectively. The durability of the bricks was investigated by 15 freezing–thawing cycles at temperatures from ?20 °C to 20 °C, and the weight loss was only 0.029% after all of cycles. Hemihydrates (CaSO₄ · 0.5H₂O) were dehydrated products from dihydrates in original PG with lower-pressure steam treatment, and hemihydrates were susceptible to absorbing the humidity and were transformed into densified re-crystallization gypsum (CaSO₄ · 2H₂O) that contributed to the final strength of bricks. Microstructural characteristics of bricks were investigated by XRD and SEM. Tobermorite was the significant hydrated product, which contributed to the strength of bricks. The use of autoclaved PG for making load-bearing wall bricks was recommended instead of conventional burnt clay bricks.     

Use of palm oil fuel ash as a supplementary cementitious material for producing high-strength concrete

The objective of this study is to investigate the use of ground palm oil fuel ash with high fineness (GPA) as a pozzolanic material to produce high-strength concrete. Samples were made by replacing Type I Portland cement with various proportions of GPA. Properties such as the compressive strength, drying shrinkage, water permeability, and sulfate resistance, were then investigated. After aging for 28 days, the compressive strengths of these concrete samples were found to be in the range of 59.5–64.3 MPa. At 90-day the compressive strength of concrete containing GPA 20% was as high as 70 MPa. The drying shrinkage and water permeability were lower than those of high-strength concrete made from Type I Portland cement. When the concrete samples were immersed in a 10% MgSO₄ solution for 180 days, the sulfate resistance in terms of the expansion and loss of compressive strength was improved. The results indicated that GPA is a reactive pozzolanic material and can be used as a supplementary cementitious material for producing high-strength concrete.     

Investigating effects of water salinity on geotechnical properties of fine-grained soil and quartz in a sandstone case study: Ajichay project in northwest Iran

The effect of water salinity on the geotechnical properties of a CL soil and mechanical properties of a quartz sandstone has been studied using samples from the Ajichay project, located in the northwest of Iran. The purpose of this investigation is to investigate the feasibility of using saline water in processing the clay core of earthen dams in this area. One-dimensional consolidation, swelling, and uniaxial compressive strength tests were performed on the soil with distilled, half-saline, and saline water. To evaluate the effect of water salinity on the sandstones placed in the abutments of the dams, the slake durability index and uniaxial compressive strength were investigated. Results indicated that the compressibility index decreased, hydraulic conductivity decreased, and uniaxial compressive strength of the soil increased with increasing water salinity. The soil swelling percent with all three waters was less than 1 % after 24 h. However, swelling percent increased by 23 % with saline water and decreased by 32 % with half-saline water. Some damage in the rock texture such as disaggregation, weathering, and corrosion of the feldspars along with the dissolution of carbonate cement was observed in thin sections after 6 months of immersion in saline water. The strength of the sandstones exposed to saline water for 5 months decreased by between 5 and 13 %.

     

Effect of metakaolin and foundry sand on the near surface characteristics of concrete

This paper deals with the effect of foundry sand (FS) and metakaolin (MK) on the near surface characteristics of concrete. A control concrete having cement content 450 kg/m³ and w/c of 0.45 was designed. Cement was replaced with three percentages (5%, 10%, and 15%) of metakaolin weight, and fine aggregates were replaced with 20% foundry sand. Tests were conducted for initial surface absorption, sorptivity, water absorption and compressive strength at the ages of 35, 56, and 84 days.Test results indicated that with the increase in MK content from 5% to 15%, there was a decrease in the initial surface absorption, decrease in the sorptivity till 10% metakaolin replacement. But at 15% MK replacement an increase in sorptivity was observed. All mixtures showed low water absorption characteristic i.e. less than 10%. Compressive strength shared an inverse relation with sorptivity. Higher MK replacements of 15% are not helpful in improving inner core durability, even though it helps in improving surface durability characteristics. Inclusion of foundry sand resulted in reduction in compressive strength. This aspect cements the findings that addition of FS causes permeability of concrete to increase causing in an increase in sorptivity and water absorption of concrete.     

Direct utilization of liquid slag from phosphorus-smelting furnace to prepare cast stone as decorative building material

Discharge of huge amount of liquid slag from phosphorus-smelting electric furnace has posed serious threat to the environment. In this study, a novel approach of directly recycling the liquid slag to prepare cast stone as decorative building material was proposed and experimentally tested. In our lab experiments, 76 wt.% water-quenched slag was re-melted at 1400 °C for 0.5 h (thus simulating liquid slag from phosphorus-smelting electric furnace), and then mixed with 18 wt.% quartz powder and 6 wt.% calcined kaolinitic clay, and subsequently melted together at 1450 °C for 1 h into modified liquid slag which was cast, heat-treated, annealed and transformed into cast stone. The optimal temperature for heat-treating cast stone ranges from 850 to 900 °C. And as-prepared samples present excellent properties of bending strength, acid resistance and alkali resistance. ESEM images show that their microstructures are composed of spherical granules with particle sizes of about 0.2–0.4 μm, which are non-crystalline as indicated by the results of XRD analysis. EDS results show that the contents of major elements in the granule are different from those in its background area. Results of TCLP test show that heavy metals from raw slag have been solidified in the cast stone. The practical feasibility of the new technology was examined further by on-site experiments, in which fresh liquid slag from phosphorus-smelting electric furnace was directly mixed with quartz and kaolinitic clay to produce cast stone. The results were quite stable and consistent with those of lab experiments, proving that the proposed approach of direct utilization of both energy and material of liquid phosphorus slag to produce cast stone as decorative building material is feasible, cost-effective and environment-friendly.