Estimation of uniaxial compressive strength from point load strength,Schmidt hardness and P-wave velocity

Uniaxial compressive strength is considered one of the most important parameters in the characterization of rock material in rock engineering practice. The study investigated correlations between uniaxial compressive strength and point load index, P-wave velocity and Schmidt hardness rebound number together with the effects of core diameter size. A total of 150 core samples at five different diameters (54, 48, 42, 30 and 21 mm) were obtained from sandstone, limestone and cement mortar. Ten saturated samples at each diameter (length:diameter ratio 2:1) were prepared from each of the three materials. The best correlations were found between uniaxial compressive strength and point load or Schmidt hammer values. The closest relationship was observed for the 48 mm diameter cores.      

Effect of micro-silica loading on the mechanical and acoustic properties of cement pastes

This study aimed at investigating the role of ultra fine sand (UFS) in enhancing the mechanical and acoustic properties of cementitious pastes. The microstructural origin of these properties was also identified and compared to the conventional materials. The maximum particle size of the UFS used was 100 μm (100% passing) while 50% of the UFS had less than 20 μm in diameter. Ordinary Portland cement (OPC) was partially substituted by UFS at 1%, 2%, 3%, 4%, 5%, 7.5% and 10% by weight of binder. The blended compounds were prepared using the standard water of consistency. Test samples with dimension of 20 × 20 × 20 mm and 40 × 40 × 160 mm were cast for compression and bending strengths tests, respectively. Circular samples with diameters of about 100 and 29 mm and average thickness of about 30 mm were used for sound absorption tests. All samples were kept in molds for 24 h, and then de-molded and allowed to cure in water for 28 days. The specimens were dried at a temperature of 105 °C for 24 h in an oven before testing. It was found that as the loading of UFS increases both the compressive and bending strength increase up to about 5% UFS loading, then a decrease in these properties was observed. This can be attributed to the pozzolanic effect of UFS resulting in enhancing the chemical reaction between free lime in cement and silica producing more hydration products that makes the paste more homogeneous and dense. In addition, the dispersed UFS has improved the filling effect allowing denser packing of the paste. These dense microstructural features were captured by scanning electron microscope (SEM) examination of the 5% UFS modified compound. The results also showed that, the sound absorption and noise reduction coefficient (NRC) for modified cement paste decreases with the increase of UFS up to 5% and this may be due to the decrease in porosity. However, the NRC began to increase at UFS loadings of 7.5% and 10% due to the increase in the porosity of the compounds.     

Nanostructured zonolite–cementitious surface compounds for thermal insulation

This paper investigates the effect of zonolite loadings on the thermal resistivity and indirect tensile strength of nanostructured cementitious compounds. The main objective of this research is to develop a structural lightweight compound that can be used on building skins and cores for pre fabricated structural insulated panels (SIPs). The application of this compound is intended to improve the thermal resistivity of the building envelope with suitable mechanical performances. The zonolite dosage was added to the cement-nano clay blend at different dosages up to 40% by weight. The nano clay reinforcement used is montmorillonite clay (Hydrated sodium calcium aluminum silicate). The mixes were prepared using water of consistence. The wet compounds were molded in PVC cylindrical molds, having 50 mm inside diameter and 27 mm height, and left for 24 h, then demolded and cured in humid air (20 ± 1 °C&100% RH) for 28 days. The samples were then dried at 105 ± 5 °C for 24 h before testing using a forced convection oven. The thermal resistivity and indirect tensile strength of the different compounds were evaluated. Results demonstrate that the thermal resistivity at 40% zonolite loading enhanced by about 2.9 folds compared to the control samples. An increase of more than 30% in the indirect tensile strength was also achieved when a 0.5% by weight of polycarboxylate superplasticizer was used.     

Investigation into effect of scratch length and surface condition on Cerchar abrasivity index

The Cerchar abrasivity index (CAI) obtained from Cerchar abrasivity tests is an indicator of abrasiveness of rocks, and widely used for the estimation of bit/cutting tool life and wear rates in various mining and tunnelling applications. The effect of scratch length on CAI is investigated in this study by use of West apparatus and 6 different steel styluses with Rockwell Hardness of HRC40-42, HRC44-46, HRC48-50, HRC50-52, HRC54-56, and HRC58-60. The tests are carried out on 15 different rock samples (sedimentary, igneous, and metamorphic) on which rough and sawn cut surfaces with scratch lengths varying between 2 mm and 20 mm with an increment of 2 mm, thus resulting in total 27,000 scratches. It is observed that the CAI values between 85% and 93% are reached at the sliding distance of 10 mm while about the final CAI value of 99% is reached at 15 mm. It is also observed that the CAI values on rough surfaces are about 18% higher than those on sawn cut surfaces. Besides, it is determined that the most suitable surface condition in CAI test is sawn cut surfaces according to the coefficient of variation of CAI values in measurement depending on the stylus hardness and the measurement surface condition.     

Strength,durability, and micro-structural properties of concrete made with used-foundry sand (UFS)

This paper presents the design of concrete mixes made with used-foundry (UFS) sand as partial replacement of fine aggregates. Various mechanical properties are evaluated (compressive strength, and split-tensile strength). Durability of the concrete regarding resistance to chloride penetration, and carbonation is also evaluated. Test results indicate that industrial by-products can produce concrete with sufficient strength and durability to replace normal concrete. Compressive strength, and split-tensile strength, was determined at 28, 90 and 365 days along with carbonation and rapid chloride penetration resistance at 90 and 365 days. Comparative strength development of foundry sand mixes in relation to the control mix i.e. mix without foundry sand was observed. The maximum carbonation depth in natural environment, for mixes containing foundry sand never exceeded 2.5 mm at 90 days and 5 mm at 365 days. The RCPT values, as per ASTM C 1202-97, were less than 750 coulombs at 90 days and 500 coulombs at 365 days which comes under very low category. Thereby, indicating effective use of foundry sand as an alternate material, as partial replacement of fine aggregates in concrete. Micro-structural investigations of control mix and mixes with various percentages of foundry sand were also performed using XRD and SEM techniques. The micro-structural investigations shed some light on the nature of variation in strength at the different replacements of fine aggregates with foundry sand, in concrete.     

Strength and toughness improvement of cement binders using expandable thermoplastic microspheres

The effect of Expandable Thermoplastic Microspheres (ETM) loading on the fracture resistance and indirect tensile strength of cement binders is studied. Portland white cement (PWC) was used as the matrix in the current study. Loadings of 0.1%, 0.35%, 0.5%, 0.75% and 1%, by weight, of ETM were added to the dry cement. Semi-circular bend specimens, 152 mm in diameter and 27 mm thickness with different notch depths were fabricated to study the crack resistance of the compounds, J_c. For the indirect tensile tests, circular specimens, 50 mm in diameter and 12.7 mm thickness were used. All specimens were left to cure under water for 7 days. A 2.5-fold increase in the indirect tensile strength was achieved at an ETM loading of 0.35% by weight. A nearly threefold increase in the fracture resistance occurred at the 0.1% ETM loading. The thermal resistivity of the compounds increased by 30% for a 1% Expancel loading. Fracture surface examination revealed that the ETM facilitated the permeation of water by creating pores. Thus, an optimum strength and fracture resistance was achieved between 0.1% and 0.4%.     

Shear bond strength between asphalt layers for laboratory prepared samples and field cores

This paper describes the laboratory measurement of shear interface properties between asphalt layers using the Leutner test. Results are presented and compared for both laboratory prepared specimens and field cores. The standard Leutner test was modified by the introduction of a 5 mm gap into the shear plane to reduce edge damage caused by misalignment of the specimen and specimens that incorporate a thin surfacing material were extended using a 30 mm thick grooved metal cylinder to eliminate dependence of the shear strength on surfacing thickness. The laboratory produced surfacing/binder course combinations incorporating the 20 mm Dense Bitumen Macadam (20 DBM) binder course showed the highest average shear strengths when nothing was applied at the interface and the lowest average shear strengths when the tack coat was applied at the interface. The average shear strength from field cores was found to increase as the class of the road increases for both surfacing/binder course interfaces and binder course/base interfaces.     

An experimental investigation into the cutting deformation mode of AA6061-T6 round extrusions

Experimental testing was completed to study the load/displacement and energy-absorption characteristics of AA6061-T6 round extrusions under a cutting deformation mode. A heat-treated 4140 steel alloy cutter was designed and manufactured with four cutting blades of approximate average thickness of 1.18 mm to penetrate through the round AA6061-T6 extrusions. The specimens utilized in this experimental investigation were tubes of lengths 200 and 300 mm with a nominal wall thickness of 3.175 and an external diameter of 50.8 mm. Results from the experimental tests showed that the cutting deformation mode exhibited a high average crush force efficiency of 0.95 compared to average values of 0.66 and 0.20 for progressive folding and global bending deformation modes, respectively. An almost constant cutting force was observed during the cutting deformation process. For both the 200 and 300 mm length tubes, the average total energy absorption was observed to be 6.11 kJ, which was independent of tube length. The mean steady-state cutting force observed was 45.58 kN and a fair correspondence was found between the theoretical predictions and the experimental results.     

Internal structure of compacted permeable friction course mixtures

Durability and functionality (i.e., noise reduction effectiveness and drainability) of permeable friction course (PFC) mixtures depend on the characteristics of the air voids (AV) contained in the mixture. This study analyzes the internal structure of PFC mixtures, assessed in terms of AV characteristics; determined using X-ray Computed Tomography and image analysis techniques. Corresponding results showed: (i) heterogeneous distributions of AV in the horizontal direction of both field-compacted mixtures (road cores) and specimens compacted using the Superpave Gyratory Compactor (SGC) and (ii) limitations to compare their vertical AV distributions. Recommendations to reduce the horizontal heterogeneity included using road cores with a minimum 152.4 mm diameter and coring SGC specimens to 101.6 mm in diameter. Implementation of field-compaction control and future analysis of mixtures prepared accordingly was recommended to determine the pattern of vertical AV distribution that should be reproduced in SGC specimens and corresponding modifications required for fabrication of these specimens.     

Energy absorption of axially compressed thin-walled square tubes with patterns

The paper suggests the introduction of patterns to the surface of conventional thin-walled square tubes to improve the energy absorption capacity under axial compressive loads. A quasi-static axial crushing analysis has been conducted numerically by the nonlinear explicit finite element code LS-DYNA. Two types of patterns constructed using the basic pyramid elements were introduced. Type A pattern was aimed at triggering the extensional mode for relatively thin square tubes whereas type B pattern was intended to develop new collapse mode capable of absorbing more energy during collapse. A total of 30 tubes with a length of 120 mm, thickness 1.2 mm and widths of 40 or 60 mm were simulated. Numerical results showed that all tubes with type A patterns developed the extensional collapse mode instead of the symmetric collapse mode and absorbed about 15–32.5% more energy than conventional thin-walled square tubes with a mass increase less than 5%. Meanwhile, a new collapse mode named octagonal collapse mode was observed for tubes with type B pattern and the energy absorption of tubes developing this mode increased by 54–93% compared with the conventional tube. The influence of various configurations of the patterns on the deformation and energy absorption of the tubes was also discussed. The paper opens up a new avenue in design of high energy absorption components.     

Applicability of the Small Diameter Sampler for Niigata Sand Deposits

Applicability of tube sampling for Niigata sand deposits is discussed through bender element and cyclic triaxial tests for samples obtained from two-chambered hydraulic piston samplers (Shogaki, 1997) with inner diameters of 48 mm and 50 mm, a one-chambered 70 mm diameter sampler, a 125-mm rotary triple-tube sampler and the frozen (FS) sampling method (Yoshimi et al., 1989). The relationship between the relative density (D_r) and normalized SPT N-value (N₁) obtained from small diameter samplers with inner diameters of 45 mm and 50 mm samplers was close to that of the FS and the N₁ coefficient was greater than those of the 70-mm and other tube samplers. The stress ratio at 20 cycles (R_L20) and the initial modulus of rigidity (G_CTX) of samples obtained from the 45-mm and 50-mm samplers were greater than those of the 70-mm, 125-mm rotary triple-tube and other tube samplers. However, the R_L20 values obtained from the 45-mm and 50-mm samplers were smaller than those of the FS sampler in the area of N₁>24. The G_BE and G_CTX values obtained from the 45-mm and 50-mm samplers were close to those of the FS sampling. Therefore, the 45-mm and 50-mm samplers can take equally high quality samples for Niigata sand deposits.     

Microstructure and durability of mortars modified with medium active blast furnace slag

Mechanical characteristics and durability properties of blast furnace slag cement composites largely depend on the hydraulic activity of the slag. In this paper, a Granulated Blast Furnace Slag with a low reactivity index is used in modifying mortar composition. Microstructure and durability of mixes containing 0%, 30% and 50% of slag as substitution to OPC are respectively compared and analyzed. Water porosity, Mercury Intrusion Porosity and pore size distribution are studied after 28, 90 and 360 days of wet curing. A qualitative microstructure analysis of mortars is proposed with Scanning Electron Microscope (SEM). The durability of mortar is evaluated through capillary water absorption and chloride diffusion tests. The results indicate a finer porosity and lower water absorption for slag mortars at old ages (90 and 360 days). Moreover, lower chloride diffusion for 50% blast furnace slag substitution is observed.     

Effect of concrete mixing parameters on propagation of ultrasonic waves

An experimental study was conducted to evaluate the effect of concrete aggregate gradation, water–cement ratio, and curing time on measured ultrasonic wave velocity (UPV). 30 × 30 × 10 cm Portland cement concrete slabs were cast for ultrasonic evaluation, while 10 cm diameter by 20 cm height cylinders were cast for compressive strength evaluation The slabs and cylinders were prepared using Portland cement and limestone aggregate. Two slabs were cast from each combination of coarse aggregate gradations and water cement ratio (0.40, 0.45, 0.50, and 0.55). Four ASTM gradations were considered, ASTM No: 8, 67, 56, and 4. These gradations have nominal maximum aggregate size 25, 4.75, 19.3, and 12.5 mm, respectively.The ultrasonic equipment used in this study was the portable ultrasonic non-destructive digital indicating tester (PUNDIT) with a generator having an amplitude of 500 V producing 54 kHz waves. The time needed to transfer the signal between the transducers was recorded and used to calculate the signal velocity, which was used as a parameter in the evaluation. Ultrasonic measurements were performed at 3, 7, 28, and 90 days after concrete casting.The results of the analysis indicated that water–cement ratio was found to have a significant effect on UPV. The UPV was found to decrease with the increase of water cement ratio. Aggregate gradation was also found to have significant effect on UPV. In general, the larger the aggregate size used in preparing Portland cement concrete, the higher the measured velocity of ultrasonic waves. Also, UPV was found to be increased as concrete curing time increased. Concrete compressive strength was found to be significantly affected by water–cement ratio and coarse aggregate gradation. Lower water–cement ratio produced higher concrete strength. Also, the concrete compressive strength increased as maximum aggregate size decreased.     

Bonding strength of wood materials bonded with different adhesive after aging test

In this study, it is aimed to describe the effects of adhesives (PVAc, Desmodur-VTKA and phenol formaldehyde) on Uludag fir (Abies Bornmüllerina M.) and Oriental beech (Fagus Orientalis Lipsky) cut tangentially and exposed to heating tests (40, 60, and 80 °C) and heating duration (30, 60 and 90 days) and controls. Consequently, when compared to control samples, the highest decrease of 26.2% in average with Oriental beech and 18.5% in average with Uludag fir was obtained with the samples bonded with D-VTKA adhesive kept for 90 days. At high temperatures phenol formaldehyde adhesives can be advised as the building material used for long terms.     

Evaluation of passive confinement in CFT columns

This paper presents the experimental results of 32 axially loaded concrete-filled steel tubular columns (CFT). The load was introduced only on the concrete core by means of two high strength steel cylinders placed at the column ends to evaluate the passive confinement provided by the steel tube. The columns were filled with structural concretes with compressive strengths of 30, 60, 80 and 100 MPa. The outer diameter (D) of the column was 114.3 mm, and the length/diameter (L/D) ratios considered were 3, 5, 7 and 10. The wall thicknesses of the tubes (t) were 3.35 mm and 6.0 mm, resulting in diameter/thickness (D/t) ratios of 34 and 19, respectively. The force vs. axial strain curves obtained from the tests showed, in general, a good post-peak behavior of the CFT columns, even for those columns filled with high strength concrete. Three analytical models of confinement for short concrete-filled columns found in the literature were used to predict the axial capacity of the columns tested. To apply these models to slender columns, a correction factor was introduced to penalize the calculated results, giving good agreement with the experimental values. Additional results of 63 CFT columns tested by other researchers were also compared to the predictions of the modified analytical models and presented satisfactory results.     

Mortars with nano-SiO2 and micro-SiO2 investigated by experimental design

This paper reports the effects of nanosilica (nS) and silica fume (SF) on rheology, spread on flow table, compressive strength, water absorption, apparent porosity, unrestrained shrinkage and weight loss of mortars up to 28 days. Samples with nS (0–7 wt.%), SF (0–20 wt.%) and water/binder ratio (0.35–0.59), were investigated through factorial design experiments. Nanosilica with 7 wt.% showed a faster formation of structures during the rheological measurements. The structure formation influences more yield stress than plastic viscosity and the yield stress relates well with the spread on table. Compressive strength, water absorption and apparent porosity showed a lack of fit of second order of the model for the range interval studied. In addition, the variation of the unrestrained shrinkage and weight loss of mortars do not follow a linear regression model. The maximum unrestrained shrinkage increased 80% for nS mortars (7 days) and 54% (28 days) when compared to SF mortars in the same periods.     

Experimental study on freezing and thawing deformation of geogrid-reinforced silty clay structure

Reinforcement can reduce soil’s frost heave (F-H), but what kind of reinforcement condition is most beneficial to control soil’s F-H if it is not clear? In this study, orthogonal experiments of freezing and thawing (F-T) to reinforced silty clay under different conditions were carried out. F-H, thaw settlement (T-S) deformation and water content of three different heights of melting clay were tested. T-S displacement was positively correlated with water content and more closely related to upper layer clay’s water content. SPSS software was used to fit the regression equation of F-H and T-S displacement expressed by various influencing factors. The top three factors influencing the F-H and T-S displacement were initial water content, reinforcement spacing, and upper pressure. Taking the lowest displacement of F-H and T-S as control target, the optimal solution of all factors and target values were obtained with MATLAB software when the freezing temperature and number of freezing and thawing cycle (FTC) and upper pressure were − 15 °C, 5 times, and 30 kPa. The lowest values of F-H and T-S displacement were 3.61 mm and − 0.514 mm, respectively, when the values of the initial water content, compaction degree, and reinforcement spacing were 16%, 90%, and 25 cm, respectively.

     

The impact of increased oxygen conditions on metal-contaminated sediments part I: effects on redox status, sediment geochemistry and metal bioavailability

In order to evaluate the effect of improved oxygen concentrations in overlying surface water on the redox status, sediment geochemistry and metal bioavailability in metal-polluted sediments a 54 days lab experiment with two different experimental treatments was conducted (90% and 40% O₂). Changes in redox potential (Eh) in the sediment were monitored over time. At 6 different time points (after 0, 2, 5, 12, 32 and 54 days) and at 4 sediment depths (0-1, 1-4, 4-8 and 8-15 cm), acid volatile sulfides (AVS), simultaneously extracted metals (SEM) and total organic carbon (TOC) were measured and metal release to overlying surface water was determined. Labile metal species in both water and sediment were measured using Diffusive Gradients in Thin films (DGT). Our results showed that elevated oxygen levels in overlying surface water led to an Eh increase in the sediment of the 90% O₂ treatment from 0 to ±200 mV while AVS concentrations in the upper sediment layer decreased by 70%. Following AVS oxidation metal availability in the pore water was highly elevated after 54 days. However, Cu remained strongly bound to the sediment during the whole experiment. Only a limited metal release to the overlying surface water was noticed, which was due to the fact that SEM_tot concentrations in the sediment did not yet exceeded AVS levels ([SEM_tot − AVS]/f_OC = 0) after 54 days. Additionally, adsorption on Fe and Mn hydroxides and particulate organic carbon also slowed down any potential metal release. Our results indicated that increasing oxygen concentrations due to general water quality improvements can enhance the mobility of trace metals which may result in the leaching of sediment-bound metals to overlying surface water, even in undisturbed watercourses.     

Distribution of fibers in SFRC segments for tunnel linings

This paper presents research results regarding the distribution of steel fibers in concrete used to build precast tunnel segments for Line 9 of the Barcelona Metro. The fiber distribution was studied using the actual fiber contents obtained by means of crushed cores drilled from different points of three full-scale tunnel lining segments. A statistical analysis determined that the fiber content in the ends of segments tends to be greater than in the central zone. The way of transporting, pouring and compacting concrete influences the fiber content and the fiber distribution across the thickness of the segment. In addition, cores with a diameter of 150 mm were found to have a lower scatter in the fiber content than smaller diameter specimens. Finally, based on probabilistic approaches, a minimum of 11 cores is proposed to control the fiber content in FRC segments.