Laboratory Testing Program Research Articles

The cracking risk of hardening concrete exposed to realistic curing temperature regimes and restraint conditions – Experimental investigations of important parameters

Early age cracking in hardening concrete can be evaluated using dedicated calculation methods. Such calculations require a wide selection of input parameters, e.g. autogenous- and thermal deformation, hydration heat evolvement, tensile strength, E-modulus, creep, cross-section dimensions, structural configuration (degree of restraint) and climatic conditions. However, several factors can affect these materials properties and input parameters, and hence the cracking tendency of the concrete. Over the recent years, early age cracking has been included in several research projects at NTNU. In this regard, various laboratory test programs on early age cracking have been performed, providing a comprehensive matrix of results and a unique opportunity for parameter studies on e.g., fly ash content, SRA-addition, aggregate type, cement batch, w/c-ratio, degree of restraint and climatic conditions. The laboratory tests comprise both mechanical testing and restrained stress tests in the Temperature-Stress Testing Machine (TSTM). The present compilation showed that in addition to the obvious effects of degree of restraint and climatic conditions, also several of the other investigated parameters had a considerable influence on the cracking tendency of the given concrete, e.g., cement-by-fly ash replacement caused a clear reduction of the cracking risk, while variations between different batches of the same type of cement highly influenced the strength, the heat evolvement, the AD development, and consequently also the cracking risk of the given concrete.

Construction of Plastic Concrete Seepage Cut-Off Wall for Polavaram Earth Cum Rockfill Dam

Abstract: Polavaram Project is being executed on River Godavari near Ramayyapeta village of Polavaram Mandal, West Godavari District, Andhra Pradesh. This multipurpose major project envisages construction of 2454m long Earth-cum-Rock fill (ECRF) dam across river Godavari near Polavaram with a maximum height of 50.32m. The proposed ECRF dam will be founded on a bed of sand. The depth of sand bed over the underlying rock strata varies from 30m to 90m at different location. To restrict the flow of seepage water through the sand bed, a plastic concrete diaphragm wall/Cut-Off wall is proposed with its top end embedded in the clay core of the ECRF Dam and the bottom end embedded into underlying hard rock. The wall was constructed of plastic concrete using panel construction method. Plastic concrete was selected to provide a seepage Cut-Off wall that has sufficient strength to withstand both static and seismic stresses beneath the new embankment, and yet is flexible enough to undergo seismic deformations, without cracking, with the surrounding soils. This paper illustrates the construction of the plastic concrete Cut-Off wall for the Polavaram ECRF dam, including the field and laboratory testing performed to confirm design wall stiffness, strength, and hydraulic conductivity requirements. The trial laboratory and field testing programs to determine plastic concrete mix design, and the QA/QC testing conducted during construction are presented. Keywords: ECRF, Plastic concrete, Cut-Off wall, Hydraulic grab, Trench cutter, Koden, Tremie

Utilization of Fine Soil as Potential Source for Core of Rock-Fill Dam

This study investigates the use of wadi sediments as a potential source for the core of rock-fill dams. The current practice utilizes clay and silty materials for the core of the rock-fill dam. In Oman, clay is not abundantly available, so there is a need to propose a local alternative material as a potential source for the core of the rock-fill dam. Dredged sediment is believed to have properties like clay but is a waste material deposited in reservoirs. The samples of wadi sediments were grouped from the reservoir of Wadi Jizzi Dam, located a few kilometers away from the city of Sohar. A detailed laboratory-testing program investigates the physical characteristics, grain size distribution, liquid and plastic limits, specific gravity, compaction, hydraulic conductivity (permeability), swelling potential, and unconfined compressive strength. All the tests were performed following the British Standard. The pure dredged sediment has a hydraulic conductivity of 7.11x10-6 cm/s, which is comparable to the requirements of the core of the dam. To improve the other properties of the dredged sediment, it is mixed in different proportions with dune sand collected from the Al-Sharqia Desert of Oman. The test results suggest that a mixture ratio of 50% of sediment to the dune sand gives optimal strength, durability, and permeability. On the other hand, for the comparison purposes, bentonite was mixed with sand by various percentage. The microscopic investigation and X-ray diffraction (XRD) analysis tests on dredged sediments suggest that the material can be utilized without causing any environmental concerns. The outcomes of this study is expected to assist the practitioners in achieving cost-effectiveness and sustainability in the design.

The impact of clay fraction on the strength and stress ratio ( K 0 ) in Gulf of Mexico mudrocks and quartz silt mixtures: implications for borehole stability and fracture gradient

Mudrock strength parameters are required to improve the prediction of fracture gradient during drilling in poorly consolidated formations. Understanding the influence that mineral composition and consolidation stress have on the mechanical properties of mudrocks aids safe well design. Small changes in the mudrock clay content are shown to have significant effects on two important engineering parameters: the lateral stress ratio at rest, K 0 , and the critical state effective friction angle, ϕ ′ cs . A laboratory-testing programme using quartz silt and a Gulf of Mexico clay mixture investigates the effects of mudrock clay content on K 0 and ϕ ′ cs at two stress levels: 1 and 10 MPa. Values of K 0 and ϕ ′ cs were obtained by subjecting composition-controlled clay–silt specimens to a drained uniaxial vertical strain ( K 0 consolidation) phase, followed by an undrained compression triaxial shear phase. Triaxial tests illustrate consistent and systematic increases in K 0 and decreases in ϕ ′ cs , with increases in clay content at both stress levels. Stress dependence is observed through increases in K 0 and decreases in ϕ ′ cs with increases in stress level. Stress-dependent behaviour is shown to be more pronounced in mudrocks of high clay content. A predictive model is presented for K 0 in normally consolidated mudrocks, as a function of clay content and effective stress. The model is used to calculate the fracture gradient (least horizontal stress) profile at the International Ocean Drilling Program (IODP) Expedition 308 Site 1324. The estimated fracture gradient illustrates the effects of clay content and consolidation stress on safe mud weight design. Thematic collection: This article is part of the Geopressure collection available at: https://www.lyellcollection.org/cc/geopressure

Numerical & experimental investigation of slotted-hidden-gap connection for square HSS brace members

The Slotted-Hidden-Gap (SHG) connection represents an attractive alternative to the conventional knife plate connection for HSS braces of steel braced frames as it allows the brace to yield along its length without having to reinforce the connection. Prior studies have proven the effectiveness of this detail for circular and square HSS braces. However, no encompassing seismic design method or detailing rules exist for SHG square HSS members. To gain deeper insight into the behaviour of the SHG connection, a preliminary numerical parametric study of square HSS braces under a monotonic tension loading protocol was done to further investigate key factors influencing the connection's performance. The weld size and length as well as the gusset plate thickness are critical in the design of SHG connections and may hinder the connection performance if poorly designed or fabricated. A laboratory testing program, of four SHG HSS ASTM A1085 (254 × 254 × 13) brace specimens with different weld configurations, was also carried out. Keeping a 20 mm overlap length despite changing the overall weld size and length was sufficient to develop the yield resistance of the braces and to force fracture away from the connection region. Utilizing longer length smaller sized welds granted an additional 3.1% of brace strains compared to connections with shorter welds.

Volumetric Mix Design Adjustments for Improving Asphalt Mixture Durability

State highway agencies (SHAs) are looking for guidance on how they can make changes to their Superpave volumetric mix design procedures to obtain higher design binder contents to improve the cracking resistance and durability of asphalt mixtures. To assist SHAs, this paper was prepared to: (a) synthesize most common adjustments made by SHAs to their Superpave volumetric mix design procedures to obtain higher design binder contents; and (b) verify the effectiveness of these adjustments through laboratory experiments. Based on a survey of SHAs, the three most common adjustments to the Superpave mix design system to obtain higher design binder contents include: lowered design gyrations (Ndesign), increased minimum requirements for voids in mineral aggregate (VMA), and lowered design air voids (including air voids regression). These adjustments were verified in a laboratory testing program which included a virgin fine-graded mixture and a 20% reclaimed asphalt pavement (RAP) coarse-graded mixture. The results suggest that lowering Ndesign may help increase the design binder content initially but mix designers can select design gradations to reduce VMA and binder content back to levels achieved with the higher Ndesign levels. The other common adjustments (i.e., increased minimum VMA and lowered design air voids) can yield higher design binder contents. However, these approaches may be ineffective if Gsb is not accurately measured during mix design or if VMA is not controlled during mix production.

Geomechanische Reservoircharakterisierung in Bayern im Rahmen der Geothermie‐Allianz Bayern

AbstractTo increase the use of geothermal energy in Bavaria, the subsurface, which serves as a reservoir, must be explored as precisely as possible. In the projects of the Geothermal‐Alliance Bavaria, the most promising areas for geothermal exploration in Bavaria were characterised based on an extensive geomechanical laboratory testing program which was carried out on both drill cores and analogue samples from quarries. In the North Alpine Foreland Basin (SE Germany), the geomechanical test results on Upper Jurassic carbonate rocks show a high heterogeneity. On the contrary, in the Franconian Basin (NE Bavaria) the geomechanical properties of granite analogues are rather homogenous. For the numerical simulation of the borehole stability, the determined parameters from ultrasonic‐ and compression tests serve as input parameters for different scenarios. For both locations, the determination of the failure depth around the borehole and the stress distribution in the near‐field of the borehole were accomplished. In the North Alpine Foreland Basin, the borehole stability decreases with increasing depth. For all scenarios in NE Bavaria, the borehole stability is very low. In the future, the determined parameter ranges will allow to validate already existing models and to develop new ones. This will enable a better knowledge of the sedimentary and crystalline reservoirs and a more effective use of geothermal energy in Bavaria.

A high-cycle accumulation model for clay and its application to monopile foundations

A high-cycle accumulation (HCA) model predicting the accumulation of permanent strain or excess pore water pressure in clay under a large number of load cycles is presented. Data from an extensive laboratory testing program on kaolin under undrained cyclic loading has been analysed for that purpose. The influence of strain amplitude, void ratio, stress ratio, overconsolidation ratio and loading frequency on the accumulation rates is considered in the constitutive equations of the HCA model. The proposed model is validated first by the simulation of element tests. Subsequently, its application to offshore wind turbine foundations under long-term lateral cyclic loading is presented by the back-analysis of a centrifuge test on a monopile in soft clay. The results are in good accordance with the measurements in terms of pile displacement and bending moment versus number of applied cycles. It is concluded that the proposed model is feasible to describe the long-term behaviour of clay subjected to high-cyclic loading.

Elevated Temperature Effects on Geotextile–Geomembrane Interface Shear Behavior

The performance of geosynthetic layered systems during their service life in terms of interface shear behavior and strength properties is of major importance in certain geotechnical applications. The interfaces between geotextiles and geomembranes in landfill applications are subject to temperature changes. In this respect, interface shear behavior requires assessment of the engineering strength properties of the components, both independently and collectively, at different temperatures. To this end, an extensive research study was undertaken to investigate temperature effects on the interface shear behavior between needle-punched nonwoven (NPNW) polypropylene (PP) geotextiles and both smooth polyvinylchloride (PVC), as well as smooth and textured high-density polyethylene (HDPE) geomembranes. A temperature-controlled chamber (TCC) was utilized to simulate the field conditions at elevated temperatures and evaluate shear displacement and frictional response mobilized at different temperatures. The physical laboratory testing program consisted of interface shear tests between material combinations found in landfill applications under a range of normal stress levels from 10 to 400 kPa and at a range of ambient temperatures from 21°C to 50°C. An increase in temperature from the standard laboratory test temperature of 21°C to an equivalent in situ temperature of 50°C increases the peak and postpeak interface friction values by a minimum of 14%. For selected combinations of materials, the amount of increase can be in excess of 20% and as high as 22%. Consequently, interface shear behavior determined at room temperature yields interface friction values that are conservative at higher temperatures.

Compressibility and consolidation properties of Santos soft clay near Barnabé Island

A geotechnical study based on characterization tests and seventy incremental loading one-dimensional consolidation tests was carried out on high-quality undisturbed samples taken from Santos Harbor Channel subsoil near to Barnabé Island, where a pilot embankment was built. The characterization profiles revealed a stratigraphy following the pattern described by Massad (2009), with a 9 m-thick fluvial-lagoon-bay sediments (SFL) clay layer. The consolidation tests were performed following two loading criteria. In criterion A (series one tests), a new loading was applied whenever the strain rate (ε) reached 10-6 s-1, the highest integer power of 10 after the “end of primary” consolidation for double drained 2 cm thick specimens. In criterion B (series two tests), the standard procedure of 24 hour-long stages was adopted. Criterion A reduced the total duration of the consolidation tests from ten to about three days. The preconsolidation (yield) stress (σ’p) and the compressibility parameters Cc and Cr obtained from “e versus σ’v (log)” compression curves of all tests are provided. Series two tests showed that the 24-hour “e versus σ’v (log)” compression curves are translated to the left of the ε = 10-6 s-1 “e versus σ’v (log)” compression curves, keeping Cr and Cc average values unchanged, but decreasing σ’p by about 8%. The SFL clay Cc/(1+e0) values obtained herein are higher than those presented by Massad (2009) due to the higher-quality samples tested in this study. It is shown that it is feasible to carry out a high-quality laboratory test program for design purposes following current standards.

Experimental study on earth pressure reduction of waste tyre bales used as a backfill for rigid retaining structures

Abstract Waste tyre-derived products, including whole tyres, tyre bales, shreds, chips and crumb rubber, have been widely used in geotechnical applications. In particular, tyre bales have considerable potential for use in the construction of a lightweight embankment or road foundation over soft ground, slope stabilisation or landslide repairs and the backfilling for retaining structures. Proper design of tyre bale structures requires a reliable strength analysis to ensure an adequate factor of safety. The analysis should utilise the properties of the tyre bales and the baled structures, which must be properly determined. A laboratory test programme was developed to determine the key strength parameters of a backfill made of tyre bales supplemented with a lightweight aggregate. Full-scale direct shear tests were conducted to define the interface shear strength between the tyre bales and the filling material. Earth pressure reduction analysis based on the experimental results was performed as well to assess the effectiveness of waste tyre bales used as a backfill for rigid retaining structures.

Evaluation and Development of Performance-Engineered Specifications for Monotonic Loading Cracking Performance Assessment Tests and Indicators

Abstract This study investigated the validity of various monotonic cracking performance assessment testing standards and indicators to describe the expected cracking performance in the field. A total number of 17 field test sections with known field cracking performance were selected and evaluated. Field cores were extracted from these sections, and a comprehensive laboratory testing program was carried out. The authors conducted four monotonic testing standards and calculated 11 performance indicators. The study findings showed that there was no direct correlation between the laboratory testing results of monotonic tests and indicators and the observed field cracking performance. The variable air void content and thickness of the extracted field cores are believed to influence the laboratory testing results of monotonic tests and indicators. Therefore, this study proposed an alternative approach to develop performance specifications (thresholds) for monotonic tests and indicators. The thresholds were developed indirectly using a correlation between cyclic testing and both monotonic tests and the observed field cracking performance. The results demonstrated the effectiveness and success of the proposed approach in developing performance thresholds. Pass/fail cracking performance assessment thresholds were proposed for various monotonic indicators to distinguish between asphalt mixes with good, fair, and poor cracking resistance. Besides, the study recommends the Weibull cracking resistance index, determined from the indirect tension test, as a simple performance indicator to assess mixes resistance to cracking.

Large-scale characterisation of cemented rock fill performance for exposure stability analysis

A novel large-scale geomechanical laboratory testing program is developed to provide full characterization of the strength and deformational response of cemented rockfill (CRF) material for use in exposure stability analyses. Uniaxial compressive strength (UCS), direct shear, and three-point bending tensile tests are performed on large-scale samples that require the use of novel processes and laboratory equipment. For the first time, the shear properties of large-scale CRF samples have been investigated using direct shear tests under constant normal stiffness (CNS) boundary conditions. Large-scale three-point bending tests are also conducted to obtain true tensile strengths without having to infer them from UCS test results. For up to 28 days curing time, the effects of particle size distribution and binder quantity are experimentally examined for each compression, tension, and shear failure mode through a study of the full stress–strain response. In order to obtain accurate laboratory results, findings are compared against published large-scale tests from various mine sites. The results show that the large-scale samples completed herein provide a reliable UCS estimate with standard deviations of less than one. It is also found that the direct shear responses are substantially larger for simulated CRF: Sidewall contacts than CRF: CRF contacts, and tensile strength responses are higher than previously estimated at 10% of the UCS strength. The effect of particle size distribution on the geomechanical response of the CRF material is highlighted through the large-scale sample testing. The findings of this research study provide increased technical understanding for the development of CRF structures in underground mines that are cost-effective, safe, and durable. Additionally, this research study establishes a practical testing methodology that overcomes the challenges that occur in collecting quantitative geomechanical data from large-scale CRF samples for design purposes.

Testing and numerical modelling of circular CFDST cross-sections with stainless steel outer tubes in bending

The structural performance of circular concrete-filled double skin tubular (CFDST) cross-sections with stainless steel outer tubes has been examined herein based on experiments and numerical modelling. A laboratory testing programme comprising a total of 22 four-point bending tests was performed on seven CFDST cross-sections with varying concrete grades. The details of the test rig and procedures, as well as the key test observations, including the failure moment capacities, moment–curvature curves and failure modes, are fully reported. A numerical modelling programme was then carried out; a finite element (FE) model was first established to replicate the test observations, and then adopted to conduct a parametric study to acquire further FE data over a broader spectrum of material strengths and cross-section slendernesses. Based on the combined set of test and FE results, the general design provisions for concrete-filled carbon steel members in the current European and American design codes were evaluated for their applicability to the studied CFDST cross-sections. Overall, the results revealed that both of the examined design codes yield unduly conservative (less so for the higher concrete grades) and scattered moment resistance predictions, though some moment resistances predicted from the European code were on the unsafe side. Modifications, including a concrete reduction factor η to reflect the reduced relative effectiveness of using higher concrete grades and a modified stress distribution considering the partial spread of plasticity, were proposed and shown to improve the consistency of the resistance predictions. Finally, the reliability of the current and modified design rules was demonstrated through statistical analyses.

IDW Interpolation of Soil Moisture Retention Curve Utilizing GIS

This search aim to analyse the Soil Moisture Retention Curve (SMRC) by spatial interpolation mapping using Inverse Distance Weighted scheme (IDW). The SMRC is a Graphical Representation the mathematical relationship between the metric suction of soil (it represents the difference between the pore of air pressure (ua), and the pore of water pressure (uw) and either soil water contents (volumetric and gravimetric) or S (degree of saturation). The soil samples were obtained from three locations of Baghdad University by drilling pits of depth 0.5 to 1 m under the ground level. An extensive Laboratory Testing Program was performed on the studied samples. Rosetta program was utilized to estimate Unsaturated Hydraulic properties from the data of surrogate soil such as the data of soil texture and bulk density. After obtaining the properties for the three soil samples applying IDW spatial interpolation techniques by utilizing the Arc Map-GIS program on a satellite image of the Landsat-8 satellite with a high recognition accuracy for studding properties for the areas surrounding calculated points.

Effect of stud material and structural properties on the transmission loss of partitions

A common light frame wall design is gypsum wall board (GWB) cladding on each side of a row of studs. Steel studs are available in a variety of metal thicknesses and designs, and wood studs can be solid lumber or engineered wood composite studs with a variety of structural properties. Most published laboratory testing on these walls uses only a small subset of the available stud types, and the acoustical effect of changes to the stud parameters is not well understood. The authors and colleagues have performed several laboratory testing programs to systematically investigate the acoustical effects of stud properties, some of which were presented at Internoise 2020. This paper analyzes the effects of stud material and structural properties on third-octave transmission loss values and single-number ratings.

Studies on Strength and Behaviour of Hot Mix Asphalt Using Steel Slag Aggregates in Pavements

Steel slag is a by-product of the steel industry. These waste materials create environmental pollution in the vicinity as they are imperishable and safe disposal of Industrial wastes is a major problem. This made engineers think about wastes that can be helpful for recycling. Based on intensive laboratory testing program, the characteristic properties of Steel Slag Aggregate (SSA) were assessed to determine its suitability to be used in Hot Mix Asphalt (HMA) and also as a potential material to be used as aggregate in flexible pavements. By utilizing this material in construction can minimize the depletion of natural resources around the world. Four different percentages (0%, 25%, 50% and 75%) of SSA were used and the proposed mix designs for HMA were conducted following the Marshall mix design. The experimental results indicate that the addition of SSA has significant improvement in the properties of HMA. An increase in density, stability and flow values and reduction in the per cent of air voids were observed in specimens prepared with above replacements. Keywords: Hot Mix Asphalt (HMA): Steel Slag Aggregate (SSA): Natural Aggregates (NA): Marshall Mix design:

Effect of textural characteristics on engineering properties of some sedimentary rocks

As it is commonly known, the estimation of physical and mechanical characteristics of rocks is very important issue in various geotechnical projects. The characteristics are mainly influenced by the microfabric-texture features of rocks. In this research, dry unit weight, effective porosity, point load index, Schmidt rebound hardness, uniaxial compressive strength, and texture coefficient were measured with the aim of correlating the physical and mechanical properties to the texture coefficient. For this purpose, a comprehensive laboratory testing program was conducted after collecting twenty sedimentary block samples including nine limestones and eleven mudstones, taken from Kalidromo (central Greece) in accordance with ASTM and ISRM standards. Also, mineralogical and petrographic properties, textural characteristics as well as X-ray diffractions were studied and the obtained results were statistically described and analysed. The maximum and minimum values of the texture coefficient were 0.13 and 0.50, respectively. The highest value was obtained for the rocks with a large amount of grains. Regression analyses were used to investigate the relationships between the texture coefficient and the engineering properties. Thus, empirical equations were developed and because of the good determination coefficients, they showed that all of the engineering properties were well correlated to the texture coefficient.

Consolidated Undrained Monotonic Shearing Response of Hydrophobic Kızılırmak Sand

Geotechnical properties of hydrophilic (wettable) sands have been widely discussed in the literature. However, sands may gain hydrophobic (non-wettable) properties after being exposed to a hydrophobic agent in the nature. The number of available studies regarding the response of hydrophobic sands is very limited, and mostly focus on their environmental and hydrological aspects. To close this gap, a controlled laboratory testing program, consisting of 18 monotonic strain-controlled consolidated undrained triaxial shear tests, was designed. Tests were performed on fully saturated hydrophilic and hydrophobic re-constituted Kızılırmak sand samples of different relative densities with pore water measurements. Hydrophobic samples were prepared by using 1 and 2 % WD-40 lubricant by mass. The effect of hydrophobic agent was assessed by comparing the stress – excess pore water pressure - strain responses of hydrophobic sand samples with those of conventional (hydrophilic) sand samples. Test results revealed that addition of hydrophobic agent increases the dilatancy of sands at low confining stresses (~100kPa) by decreasing the excess pore water pressure generation. At higher confining stresses (~400kPa) this effect is less pronounced. Moreover, the addition of hydrophobic agent up to 2% by mass does not systematically and significantly change the effective angle of shearing resistance of sand samples, independent of their initial relative density and confining stress levels.

Evaluation of the slotted-hidden-gap (SHG) connection for square HSS brace members

Hollow structural section (HSS) braces of concentrically braced steel frame structures are often connected using a knife connection, which creates a net area in the brace due to the slot. Tensile rupture of the brace's net section is the controlling failure mode unless reinforcing schemes are utilized. The “Slotted-Hidden-Gap (SHG)” connection, in which a notch is created in the gusset plate to overlap the gross area of the tube to eliminate the net area, represents an attractive alternative to traditional connection reinforcements; however, no design guidelines exist for the SHG connection for square HSS braces. A laboratory testing program and finite element modelling were carried out to determine the minimum overlap length required to develop the yield resistance of a square HSS brace. The test program included monotonic tensile loading tests on short conventional- and SHG- connection specimens, and one reversed cyclic loading test on a 4.86 m long brace specimen with SHG connections. An overlap length of 5% of the weld length was sufficient to develop the yield resistance of the braces with SHG connections. For those specimens, the HSS eventually fractured on their gross area away from the connections, after experiencing extensive yielding along their length. Conversely, braces with the conventional connections suffered localised yielding and fracture at the net section. The long brace with SHG connections attained its yield tensile resistance, including a 15% increase due to strain hardening, while sustaining an axial deformation corresponding to a storey drift of 3.14%.