Substitution of Recycled Plastic Aggregates (RPA) in concrete and its influence on pullout capacity of mechanical and chemical anchors

There is a lot of plastic going to land fill or entering environmentally sensitive systems, that could ideally be converted into a form or material that would be considered as a resource. Much of this plastic waste is not suitable for re-cycling or use, where exposed to sun light or weathering elements. Some of these materials have been converted to granular materials and used in sub-soil drainage systems as free draining materials and as substitute for aggregates in concrete pavements. There is significant enthusiasm for utilising ‘environmentally friendly’ construction systems and materials. Unfortunately, that enthusiasm can result in them being utilised in in-appropriate situations that can have a negative result to the reputation of the material or system. The aim of this project was to determine if anchors and fixings inserted into Recycled Plastic Aggregates (RPA) concrete elements will perform as expected and required. Proprietary RPAs were procured from a commercial supplier to substitute for natural concrete aggregates in various proportions. Normal and RPA concrete cylindrical samples were manufactured in a controlled environment at USQ lab and subsequently cured for 28 days. The purpose of manufacturing and testing normal concrete samples, involving standard concrete blends, was to provide a reference point when comparing the performance of the RPA concrete systems. Compression tests were performed on both normal and RPA concrete samples using the universal load test machine. On the other larger samples, holes were drilled in the normal and RPA concrete samples to install proprietary mechanical and chemical anchors so pull-out tests could be performed to simulate real life scenario. These pull-out tests were also performed on universal load test machine. The 50% RPA concrete demonstrated significant capacity reduction and to the extent that these rates cannot be sustainable. The 20% RPA concrete has demonstrated reduction in capacities that could conceivably be tolerated in the construction industries. The mechanical anchors were noticeably more affected by the RPA substitution than the chemical anchors. The substitution of recycled plastic provides a sustainable option for offsetting waste plastic going to landfill, thereby reducing environmental pollution. This study develops confidence in the performance of post fixed anchors inserted into low percentage RPA concrete, creates awareness in the industry and supports recycling through buying products which include recycled content in line with Australian Government National Plastic Plan 2021

Shear strength properties of clean and clay infilled rock joints: an analysis of the impast of moisture content under CNL conditions

Rock joints are a type of fracture or discontinuity that have little or no movement that is parallel to the plane of fracture caused by forces acting perpendicular to the fractured walls, where the opening of the break is parallel to the face of least resistance. These are common phenomena in geology around the world and range from small scale to tectonic fault lines. The first part of this project focused on the effect of clean rock joints on the shear strength of the joint at normal loads of 100, 300, 500 and 700 kPa. Rock joints leave an opportunity for infill to occur in the form of soil, water, or mineral precipitates. The second part of this project focuses on the effects of sodium bentonite clay infill with moisture contents of 0%, 10% and 16% and normal stresses of 100, 300, 500 and 700 kPa on the shear strength properties of rock joints. As shear strength is a controlling factor for slope stability, it is important to continue research into this area in order to optimise future engineering project outcomes. There are two main loading conditions for the direct shear testing of rock joints; Constant Normal Loading (CNL) and Constant Normal Stiffness (CNS). As CNL and CNS conditions are representative of different real-world applications it is critical to understand the scope and context of each investigation. This project was conducted under the CNL boundary condition as it predominately focuses on the impact of moisture content on the shear strength of rock joints under unsaturated conditions. These conditions are more likely to occur in shallow rock formations due to the infill and moisture fluctuations that are caused by water infiltration and precipitation

Development of a wireless system to measure the strain/deformation of rock bolts

In this study a smart set-up integrated with rock bolts was proposed to automatically monitor, record and analyse rock mass deformation. The proposed system which includes sensors and a wireless data acquisition system, rapidly and readily generates data sets along with customisable graphs, calculations and analysis in a cloud system and can be used in modern mining. To evaluate the developed technique, rock bolts were instrumented lengthwise using resistive strain gauges and then connected to the wireless data logger system. Elastic tensile tests as well as pull-out tests were conducted and the strain values along the rock bolts were successfully and accurately measured, recorded and uploaded to the cloud system

Strength properties of grout for strata reinforcement

An experimental study was carried out on grout samples prepared from both Stratabinder and BU100 cementitious products. Samples were prepared with various water to grout ratios and tested for uniaxial compressive and shear strength. Triaxial tests were performed on cylindrical samples to determine values for internal friction angle, cohesion and tensile strength. It was found that the water to cement ratio affects the uniaxial compressive and shear strength of grout. The triaxial test indicated that both internal friction angle and cohesion of Stratabinder do not differ significantly from BU100

Shear behavior of clayey infilled rock joints having triangular and sinusoidal asperities

Rock joints govern an important role in the overall stability of rock slope which may be filled with infill material due to transported materials with water, weathering as well as joint shearing. There are two methods of testing rock joint shear behavior, one is Constant Normal Load (CNL), and another is Constant Normal Stiffness (CNS). The CNL is found suitable in slope stability where sliding mass can move freely without any restriction while CNS is suitable in underground excavation, pile socketed in rock and reinforced rock slope where the stiffness of boundary restricts dilation during the shearing process. This study investigates the shear behavior of clay infilled rock joints with triangular and sinusoidal asperities under CNL conditions. The pair of triangular and sinusoidal asperities is Type 1T, Type 2T and Type 1S, Type 2S respectively where prefix represent asperity height and suffix represent the type of asperity. Joint Roughness Coefficient () obtained from back-calculation of Barton equation using experimental data is 7, 9, 9 and 12 for Type 1T, Type 2T, Type 1S and Type 2S respectively. The direct shear test was performed on two campaigns, among these, was one of understanding shear behavior of infilled rock joints under various normal loads and another was the shear behavior of infill rock joints under various infill thicknesses. During the first campaign shear behavior of clayey infilled rock joint fewer than three different normal loads were tested. Likewise, in the second campaign shear behavior of clayey infill rock joint under three infill thickness were performed. Overall this study provides better insights into shear behavior clayey infilled rock joints having different joint morphology

Finite element modelling of fully encapsulated cable bolts in laboratory large scale pull out test

Modelling cable bolts in numerical software is a challenging task. Cables are made from multiple strands wound together and when loaded, they tend to act in a way more complex manner than rock bolts. This study used laboratory data from large scale pull out testing of fully encapsulated cable bolts using cementitious grout. A finite element method was adopted and a series of engineering simplifications and assumptions were made to increase the efficiency of the model. The results were able to illustrate a better capability in modelling the bulbed cables compared to the plain cables. Also, the sensitivity analysis proposed that increasing cable diameter for a given hole size (decreasing grout annulus thickness) can increase the overall peak load value, similar to an increase in concrete confinement, grout uniaxial compressive strength, and bulb size

Static and dynamic tendon pull-out test research at the University of Wollongong

Tendon technology is widely used for strata control in underground coal mines, in both primary and secondary support systems. The understanding of how they work is crucial to effective strata reinforcement design. Research on tendon technology is an evolving study and this paper is aiming at maintaining this evolution by continuing research on load transfer mechanisms under both static and dynamic conditions, which was reported initially by (Anzanpour, 2021) in ROC2021. This programme of study includes testing of different strength capacity cable bolts, which have been important in the stabilisation of the ground around mining excavations affected by rock bursts and ground seismicity. The aim of the study was to evaluate tendon performance in different loading environments. From a series of tests carried out in the most recent study, it was found that in pull testing, the load transfer characteristics vary with respect to the type of testing. The required dynamic energy for pulling-out a cable bolt can be between 50-80% lower than the static load, based on the cable type and its geometry (Plain or Bulbed). Debonding and pullout mechanisms regardless of loading rate, seem to be similar in both static and dynamic tests, however, plain cable bolts behave differently from bulbed cable bolts in reaction to pull-out load

SPT-CPT correlation in Southeast Queensland, Australia

Among the most popular in situ investigation techniques for identifying subsurface strata, cone penetrometer testing (CPT) and standard penetrometer testing (SPT) are employed in geotechnical engineering. In fact, both tests are adopted to correlate a wide range of geotechnical parameters in various design applications. The cost associated with conducting both in situ tests at the same locations often results in one method being chosen over the other. Hence, engineers have to corelate one of the tests’ parameters into the other test using empirical correlation in translating SPT blow counts (SPT-N) into CPT cone tip resistance (CPT-qc). However, disadvantages of this in situ test are that it does not directly quantify geotechnical parameters but uses correlations which are significantly influenced by soil properties. Also, many of correlations do not provide sufficient background on the statistical approach. This study investigates the conformity of the empirical correlations against local SPT-CPT correlation for different soil occurrences in Southeast Queensland (SEQ), adopting a linear regression model to validate the degree of the relationship. Seven soil groups were classified in SEQ, comprising cohesionless and cohesive soil. The results of the SEQ samples showed a strong liner relationship (r = 0.69 – 0.89) with at least 50% of data points coinciding with the regression line (R2 = 0.48 – 0.80). It follows that for some soil groups, the published correlation agrees well with the SEQ study, while others did not

Probabilistic risk assessment of acid mine drainage generation resulted from chalcopyrite oxidation process within Sarcheshmeh copper mine tailings

A probabilistic predictive method for estimating the risk of acid mine drainage generation within the copper tailings dump of the Sarcheshmeh copper mine, Iran, has been presented in this paper. For this purpose, the input and output parameters were determined after gathering historical data and building an appropriate database. Some of the critical parameters, including depth, and concentrations of bicarbonate, chloride, nitrate, and nitric, were considered input data, while the output parameters were chalcopyrite, pH. The best distribution functions on each input parameter were found by Chi Sq. criteria. Subsequently, the best linear statistical relationships between the input and output data were determined. Then, the best probability distribution functions of output parameters were defined by inserting the input parameters in the obtained linear statistical relationship. The results showed that the remaining chalcopyrite fraction values were between 0.1094 % and 0.2159% at a 90% probability level. In contrast, the pH values would be expected between 3.13 and 8.04 at this probability level

Predicting the pyrite oxidation process within coal waste piles using multiple linear regression (MLR) and teaching-learning-based optimization (TLBO) algorithm

Coal mining often leads to significant environmental hazards and health concerns when sulfide minerals, particularly pyrite, are associated with coal waste. The oxidation of pyrite typically generates acid mine drainage, a significant problem. This paper presents two mathematical relationships using a teaching-learning-based optimization (TLBO) algorithm for predicting pyrite oxidation and pH changes within a coal waste pile from Alborz-Markazi in northern Iran. A dataset was built based on historical data to achieve this goal. Some influential parameters comprising the depths of the various samples, oxygen fraction, and bicarbonate concentrations were considered as input data, while the outputs were pyrite content and pH. Then, the best statistical relationships were suggested between input and output parameters employing curve and surface fitting methods. Afterward, two multiple linear regression (MLR) models were presented for predicting pyrite content and pH. Also, two relationships have been suggested for predicting the same outputs by applying the TLBO algorithm. Comparison of the results of the latter method with the results obtained using the statistical technique, including correlation coefficient and root mean squared error (RMSE), revealed that the TLBO could predict the outcomes better than the MLR