Heavy-metal contamination in soils has become a serious environmental problem. Among all metals, excessive amount of zinc was released to soils over the years. Zinc is not only toxic to human being, but also to plants. High concentration of zinc is extremely phytotoxic. Currently, the most popular method to remediate heavy-metal contaminated soils is stabilization/solidification (S/S) technique as it is cheaper, faster and more effective to remediate heavy metals than other remediation methods. Portland cement is the most-used binder in S/S technique. However, the production of Portland cement has released a significant amount of carbon dioxide, which strongly contributes to global warming. In addition, zinc retards the setting and hydration of Portland cement, which would require more Portland cement to remediate zinc-contaminated sites. Therefore, researchers are looking for new materials to improve the performance of Portland cement in zinc-contaminated soils. In recent years, the application of graphene-based materials in concrete had proved to be effective. Due to relative cost-effectiveness and comparable properties, multi-layer graphene, known as graphene nanoplatelets, may show a promising potential in construction. Moreover, research has reported that graphene nanoplatelets can be exfoliated from graphite and potentially scaled up for full-scale applications. At present, there is no application of graphene nanoplatelets in the S/S of contaminated soils and the roles of graphene nanoplatelets in cement-stabilized zinc-contaminated clay remained unknown. In this research, graphene nanoplatelets were dispersed in solution with a high-shear mixing apparatus. Dispersed graphene nanoplatelets solution was then applied to zinc-contaminated soil along with cement. To evaluate the efficacy of this S/S method, various influencing factors such as mixing sequence, graphene nanoplatelets content, zinc content, cement content, and curing time were studied. An optimum graphene nanoplatelets content was determined through the unconfined compressive strength (UCS) of the stabilized/solidified samples. It was found that at the optimum content, the unconfined compressive strength of cement-stabilized zinc-contaminated clay was improved by 22.3% with the addition of graphene nanoplatelets. Also, graphene nanoplatelets were effective at moderate zinc content and low cement content. Graphene nanoplatelets accelerated cement hydration effectively at early ages. Microstructural analyses indicated that more hydration products were developed in samples with graphene nanoplatelets. At current stage, it is still expensive to apply graphene nanoplatelets in S/S technique; however, it is possible to exfoliate graphite into graphene nanoplatelets in future research. / Graduate / 2022-05-12

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / This study uses analytical solutions to assess a hydraulic fill model based on weathered granitoid to increase underground opening stability and mitigate rock bursts during mining operations in a conventional underground mining company located in the Coastal Batholiths of the Peruvian Andes. This study assesses the previous geological database provided by the mine, analyzes the on-site strengths produced by the exploitation works that will subsequently be filled, identifies the quality of the material used in the landfill (granitoids) through laboratory tests, and compares compressive strength at different depths, all contemplated within the landfill model used. This study focuses on the applicability of hydraulic fills in conventional underground mine using natural geological material such as granitoid. / Revisión por pares

This thesis presents the results of an investigation of factors which influence the geotechnical properties of frozen mine backfill (FMB). FMB has extensive application potential for mining in permafrost areas. The uniaxial compressive strength (UCS) of hardened backfill is often used to evaluate mine backfill stability. However, the deformation behaviour and stiffness of the FMB are also key design properties of interest. In this thesis, uniaxial compressive tests were conducted on FTB and FCPB samples. Information about the geotechnical properties of FMB is obtained. The effects of FMB mix components and vertical compression pressure on the geotechnical properties of FMB are discussed and summarized. An optimum total water content of 25%-35% is found in which the strength and the modulus of elasticity of the FTB are 1.4-3.2 MPa and 35-58 MPa, respectively. It is observed that a small amount (3-6%) of cement can significantly change the geotechnical properties of FTB.

Cross-Laminated Timber (CLT) has recently become a popular construction material for building timber structures. One advantage of CLT is, that it can be used as floor, beam and wall element. As the arrangements of layers in CLT is in perpendicular direction to each other, it exhibits remarkable strength properties in both in-plane directions. However, the low stiffness and strength properties in compression perpendicular to the grain hinder application of CLT in high rising building, since forces are usually transferred from the wall elements through floor elements perpendicular to the grain. Thus, the aim of this thesis is to get a thorough understanding of the mechanical properties of such connections for different setups, including wood-wood connections, connections with acoustic layers and connections with screws. In addition, the wall was place at different positions on the CLT-floor element. Mechanical tests and numerical simulations, by means of finite element modelling (FEM) were carried out. CLT floor elements, consisting of 5-layers, were loaded by 3-layered CLT wall elements. Displacement and deformation were continuously measured by Potentiometers/LVDTs and an optical measurement system, respectively. Based on the experimental results compressive strength, slip curve and stiffness of the CLT connections were evaluated. Subsequently, results from FE-modelling were compared with experimental findings, which show a good agreement in elastic stiffness. Experimental results exhibited a pronounced influence of the wall position and connection setup on strength and stiffness. Central position of the wall showed higher mechanical properties than edge position. Highest strength and stiffness were found for screwed connections, where the wood-wood connections showed similar results. Connections with acoustic layers exhibited the lowest mechanical properties.

There are approximately 4000 railway bridges in Sweden managed by the Swedish Administration of Transport (Trafikverket), of which a common construction type is the reinforced concrete (RC) trough bridge, which is a structure that consists of a slab carried by two longitudinal main beams which transfer loads towards the supports. A substantial amount of the RC trough bridge population is approaching the end of their service lives which consequently implies that the replacement of some of these bridges can be expected in the near future. Extending their service lives can yield positive effects from a financial- as well as an environmental perspective, and therefore it is highly beneficial to evaluate their capacities as realistically as possible. One factor that may help improve accuracy during the determination of their capacities is an evaluation of how it is affected by the location of the railway track on the bridge.  In current design codes defined by Trafikverket, consideration is taken to horizontal track displacement for a minimum displacement of 0.1 m if there doesn’t exist data suggesting that a larger displacement is prevalent on the bridge. However, Trafikverket has received data which suggest that a considerable number of bridges could experience load eccentricities which exceed the standard minimum value. This raises the question whether or not 0.1m is the most optimal limit value for load eccentricity on railway bridges. For RC trough bridges, a larger load eccentricity may result in one main beam carrying a larger portion of the load which will decrease the axle load which the bridge can carry. It is therefore important to evaluate the influence of larger horizontal displacements than what is currently is considered as a preventive action.   In addition, several studies on Swedish concrete bridges constructed during the 20th century have pointed to a significant increase in concrete compressive- and tensile strength over time. This suggests that it is possible that a considerable amount of RC trough bridges have a higher capacity than what was originally intended, and further research is required in order to understand the behaviour of these bridges when key material parameters are altered.        There are three main tasks which this master thesis seeks to complete. The first part is a detailed analysis of a database named BaTMan (Bridge and Tunnel Management) that belongs to Trafikverket. In this analysis parameters such as span length, age, material type and damages for every identified railway bridge is extracted and further processed in Microsoft Excel in order to gain a clear overview of the RC trough bridge population. The second task regards the development of a non-linear finite element model of a typical RC trough bridge named Lautajokki. The model is analysed using ATENA Science and its behaviour is verified against test results obtained during a full-scale test of the bridge performed by Paulsson et al. (1996). The last task is to use the devolved model to perform a parametric study where the effects of changes in load eccentricity, compressive strength as well as tensile strength is studied.

Ultra-high performance concrete (UHPC) has progressively gained interest because of its favorable strength and durability properties. Literature shows that curing temperature has a significant effect on the resultant mechanical properties of UHPC, generally resulting in increased compressive strength. However, limited datasets are currently available to ascertain the degree of change related to compressive strength as a function of curing temperature and conditions. This study investigates the effect of isothermal and submerged curing temperature conditions, ranging from 10°C to 90°C, on the compressive strength and elastic modulus development of UHPC and generates a numerical model to capture these effects. The extent and rate of compressive strength development in Cor-Tuf UHPC was found to increase with curing temperature, while only the rate of elastic modulus development increased with curing temperature. The numerical model shows reasonable agreement when compared with the experimental results and was successfully implemented in finite element analysis software.

Sulfide soils are silty soils, often found in saturated conditions, under the groundwater level. Characteristics of these soils, including particle size distribution and consistency limits along with chemical composition and environmental properties, cause excavation to be necessary for construction purposes. The excavated sulfide soil usually is transported and deposited in landfills. These soils are either deposited in saturated conditions or chemical buffers are added to the soil to prevent acidification. Special conditions of these landfills complicate the disposal procedure and the landfill maintenance which makes those financially expensive. Reusing sulfide soil in construction is a solution to reduce the expenses related to the management of sulfide soils. Since the mechanical properties of these soils are not suitable for construction purposes, the first step is to improve soil characteristics to the level that fulfills the needs of construction applications. One solution to improve the mechanical properties of the soil is adding a binder to the soil. The main focus of the research was to improve the mechanical properties of soil. The research activities were divided into two parts. The first part was conducted in a laboratory environment to develop mixtures, while the second focused on transferring the results to field conditions. The laboratory tests included mixing soil and binder i.e., cement was added to the soil at different percentages to evaluate the soil improvement. An unconfined compressive strength (UCS) test was conducted on the stabilized sample to evaluate the efficiency of the stabilization. The resultsof UCS for the stabilized samples were compared. Since the soil contains a high amount of water, the traditional sample preparation was not suitable. Therefore, an alternative method was developed and evaluated. Moreover, the effect of curing time on the strength and consistency limit of stabilized samples was evaluated. At last, the effect of different variables, including porosity, binder content and initial water content, on the UCS of soil was investigated to identify potential correlation between UCS and different soil variables. The results of the tests showed that adding a binder, regardless of the type of sulfide soil, positively affects the UCS of prepared samples and increasing the curing time increased the UCS of the samples. At higher cement content, the effect of curing time was more significant. Also, it was shown that at higher water content, the effect of binder is lower in comparison with the same soil at lower water content. By lowering the water content, the strength of stabilized soil reaches a maximum and drying further the soil, below the optimum water content, led to strength reduction. A correlation between UCS of sample and porosity/binder ratio was employed to predict the strength behavior of stabilized soil based on variables such as porosity, initial water content and binder dosage. In order to evaluate if laboratory results can be applied to geotechnical applications, the second part of this research included a field mixing experiment for a large-scale mixture of soil and cement. The effect of the mixing procedure with common equipment on the homogeneity of industrial-size mixture was investigated. A sampling strategy for collecting representative samples of mixture was selected and assessed. the number of mixing steps and the effect of binder dosage on the uniformity of samples were studied. Results of UCS of samples prepared from field and laboratory mixture were compared and evaluated. A field evaluation was conducted to determine the quality of the mixture and how many mixing steps are required to reduce variability between samples. Two different percentages of binder were added to the 5 Tons of soil. The UCS test samples were prepared from the soil-cement mixture in the same way as they were prepared in the laboratory and cured for a specific time. The UCS test was conducted on cured samples. The test results were compared to evaluate the mixture homogeneity in the field. The results showed that homogeneous mixtures can be obtained in the field with the available equipment. Assessing the sampling strategy showed that increasing the sampling sections from 5 to 12 and preparing single UCS sample from the collected soil provides representative samples from the soil mixture pile. Additionally, it was shown that by increasing mixing steps from 2 to 3, it was possible to eliminate samples with notable lower strength than average UCS. A greater number of mixing steps improves homogeneity while reducing the average UCS. It was found that mixing soil and binder in the laboratory improves strength better than mixing them in the field. When applying laboratory results to field design, this point must be taken into account.

The purpose of this research was to investigate the effects of reclaimed asphalt pavement (RAP) content and cement content on the strength and durability of recycled aggregate base materials. Specifically, the unconfined compressive strength (UCS) and final dielectric value in the Tube Suction Test (TST) were measured in a full-factorial experimental design including five RAP contents, five cement contents, and three replicate specimens of each possible treatment. Specimen mixtures consisted of 0, 25, 50, 75, or 100 percent RAP and 0.0, 0.5, 1.0, 1.5, or 2.0 percent Type I/II Portland cement. Both the RAP and base materials were sampled from the I-84 pavement reconstruction project performed in Weber Canyon near Morgan, Utah, during the summers of 2004 and 2005. The laboratory testing procedures consisted of material characterizations, specimen preparation, and subjection of the specimens to strength and durability testing, and the data were evaluated using analysis of variance (ANOVA) testing. Both the RAP and base materials included in this research were determined to be non-plastic, and the AASHTO and Unified soil classifications for the RAP material were determined to be A-1-a and SM (well-graded sand with gravel), respectively, and for the base material they were A-1-a and SW-SM (well-graded sand with silt and gravel), respectively. The optimum moisture contents (OMCs) for the blended materials were between 5.6 and 6.6 percent, and maximum dry density (MDD) values were between 129.7 and 135.5 lb/ft3. In both cases, decreasing values were associated with increasing RAP contents. The results of the ANOVA performed on the UCS data indicate that UCS decreases from 425 to 208 psi as RAP content increases from 0 to 100 percent and increases from 63 to 564 psi as cement content increases from 0.0 to 2.0 percent. Similarly, the final dielectric value decreases from 14.9 to 6.1 as RAP content increases from 0 to 100 percent and decreases from 14.0 to 5.8 as cement content increases from 0.0 to 2.0 percent. With design criteria requiring 7-day UCS values between 300 and 400 psi and final dielectric values less than 10 in the TST, the results of this research suggest that milling plans should be utilized to achieve RAP contents in the range of 50 to 75 percent, and a cement content of 1.0 percent should be specified for this material. Cement contents less than 1.0 percent are not sufficient to stabilize the material, and greater cement contents may cause cracking. Because control of the actual cement content in the field depends on the contractor's equipment and skill, inspection protocols should be implemented during construction to ensure high-quality work. Additional recommendations are associated with the construction process. The specimens prepared in this research were compacted to relative densities of 100 percent using modified Proctor energy. Therefore, field compaction levels must approach these density values if the same material properties are to be achieved. In addition, all specimens tested in this study were cured at 100 percent relative humidity. Following compaction in the field, cement-treated layers should be moistened frequently during the first few days after construction or promptly sealed with a prime coat or wearing surface to ensure that the cement continues to hydrate. Variability in RAP and cement contents should also be minimized to achieve consistent material properties.

The use of recycled concrete material (RCM) as pavement base material is a promising but unproven technique for road rehabilitation and construction. A telephone survey conducted to investigate the state of the practice concerning RCM usage in Utah County revealed that RCM is infrequently used in this application due primarily to a lack of practical knowledge about the engineering properties of the material. Therefore, this research was aimed at evaluating the physical properties, strength parameters, and durability characteristics of both demolition and haul-back sources of RCM available in Utah County for use as pavement base material. The study included extensive laboratory and field testing. Laboratory tests included California bearing ratio (CBR), unconfined compressive strength (UCS), stiffness, freeze-thaw cycling, moisture susceptibility, abrasion, salinity, and alkalinity evaluations. Non-destructive testing was utilized in the field to monitor seasonal variation in stiffness of an RCM pavement base layer over a 1-year period. The testing included a dynamic cone penetrometer, ground-penetrating radar, a heavy Clegg impact soil tester, a soil stiffness gauge, and a portable falling-weight deflectometer. The laboratory testing indicated that the demolition material exhibited lower strength and stiffness than the haul-back material and reduced UCS loss after freeze-thaw cycling. However, the demolition material received a moisture susceptibility rating of good in the tube suction test, while the haul-back material was rated as marginal. Both materials exhibited self-cementing effects that led to approximately 180 percent increases in UCS over a 7-day curing period. Seven-day UCS values were 1260 kPa and 1820 kPa for the demolition and haul-back materials, respectively, and corresponding CBR values were 22 and 55. The field monitoring demonstrated that the RCM base layer was susceptible to stiffness changes due primarily to changes in moisture. In its saturated state during spring testing, the site experienced CBR and stiffness losses of up to 60 percent compared to summer-time values. RCM compares well with typical pavement base materials in many respects. Given the laboratory and field data developed in this research, engineers should be able to estimate the strength and durability parameters of RCM needed for pavement design.

Frost heave is a primary mechanism of pavement distress in cold regions. The distress exhibited is dependent on the frost susceptibility of the soil within the depth of frost penetration, the availability of subsurface water, and the duration of freezing surface temperatures. Cement stabilization is one technique used to mitigate the effects of frost heave. The tube suction test (TST) is one possible method for determining the frost susceptibility of soils in the laboratory. The purpose of this research was to assess the utility of the TST for identifying non-frost-susceptible (NFS) materials stabilized with cement. This research investigated two aggregate base materials from Alaska that have exhibited negligible frost susceptibility in the field. The unconfined compressive strength (UCS), final dielectric value in the TST, and frost heave at three levels of cement treatment and in the untreated condition were evaluated for both materials. The data collected in this research indicate that, for the two known NFS materials included in this study, the TST is a good indicator of frost heave behavior. The total heave of the untreated materials was approximately 0.15 in. at the conclusion of the 10-day freezing period, which classifies these materials as NFS according to the U.S Army Corp of Engineers. Both materials had final dielectric values of less than 10 in the TST, indicating a superior moisture susceptibility rating. The results of this research suggest that the TST should be considered for identifying NFS materials, including those stabilized with cement. Additional testing should be performed on known NFS materials stabilized with cement and other additives to further assess the validity of using the TST to differentiate between frost-susceptible and NFS materials. Consistent with previous studies, this research indicates that, once a sufficient amount of cement has been added to significantly reduce frost heave, additional cement has only a marginal effect on further reduction. Therefore, to avoid unnecessary expense in construction, the minimum cement content required for preventing frost heave should be identified through laboratory testing and specified by the engineer. In this work, UCS values ranging between 200 psi and 400 psi after a 7-day cure were typically associated with this minimum cement content. Because the scope of this research is limited to two aggregate base materials, further testing is also necessary to validate this finding.