Search Results (58)

High concrete gravity dams, particularly Roller-Compacted Concrete (RCC) types, face long-term safety challenges due to weak interlayer formation and crack propagation. This study presented a comprehensive evaluation of safety monitoring indexes for the Guxian high RCC dam (currently under construction) using both numerical and mathematical models. A finite element method (FEM) is employed with a strength reduction approach to assess dam stability considering weak layers. In parallel, a fracture mechanical model is used to investigate the safety of the Guxian dam based on failure assessment diagrams (FADs) for calculating the safety factor and the residual strength curve for calculating critical crack depth for two different crack locations, single-edge and center-through crack, to investigate the high possible risk associated with crack location on the dam safety. Additionally, the Guxian dam’s resistance to hydraulic fracture is assessed under two fracture mechanic failure modes, Mode I (open type) and Mode II (in-plane shear), by computing the ultimate overload coefficient using a proposed novel derived formula. The results show that weak layers reduce the dam’s safety index by approximately 20%, especially in lower sections with extensive interfaces. Single-edge cracks pose greater risk, decreasing the safety factor by 10% and reducing critical crack depth by 40% compared to center cracks. Mode II demonstrates higher resistance to hydraulic fracture due to greater shear strength and fracture energy, whereas Mode I represents the most critical failure scenario. The findings highlight the urgent need to incorporate weak layer behavior and hydraulic fracture mechanisms into dam safety monitoring, and to design regulations for high RCC gravity dams. Full article

In this study, the effects of different fiber types on improving the high-temperature performance of roller-compacted concrete (RCC) were comprehensively investigated. For this purpose, 60 mm long steel (S), polypropylene (PP), and environmentally sustainable waste steel (WS) fibers were incorporated into RCC at volumetric ratios of 0%, 0.25%, 0.50%, 0.75%, 1.00%, and 1.25%. The prepared specimens were exposed to controlled conditions at 25 °C (room temperature), 300 °C, 600 °C, and 900 °C, and the influence of thermal exposure on compressive strength and permeability characteristics was thoroughly evaluated. The findings revealed that high temperatures led to significant changes in the physical and mechanical properties of the concrete. Notably, at elevated temperatures such as 600 °C and 900 °C, S and WS fibers were found to reduce strength loss by limiting the propagation of microcracks within the concrete matrix. However, PP fibers were observed to lose their effectiveness at high temperatures due to melting in the range of approximately 160–170 °C, which negatively affected mechanical performance. One of this study’s key findings is that waste steel fibers offer a sustainable alternative while exhibiting comparable performance to conventional steel fibers. These results highlight the potential of recycling industrial waste to reduce environmental impact and lower overall costs. Full article

Roller-compacted concrete (RCC) is designed with consideration for construction machinery capabilities, offering benefits such as rapid construction and cost-efficiency. Therefore, RCC is appropriate for large-scale concrete projects such as gravity dams. Due to its lower cement content and heat of hydration, RCC also saves energy. In this study, the compressive strength properties and mixing ratio of RCC were investigated through experiments and the results were compared with those of traditional concrete (ordinary Portland cement, OPC). In the same water–cement ratio, RCC uses less binder but achieves a higher compressive strength than OPC. Furthermore, for a strength of 210 kg/cm² at 28 days, water–binder ratios of 0.5 and 0.6 with 50 and 30% fly ash replacement rates were experimented with. The two ratios showed similar performance and economic advantages with the RCC cement content ranging from 80 to 150 kg/m³. RCC with fly ash is a cost-effective and efficient solution for large-scale projects. Full article

Roller compacted concrete (RCC) is a relatively stiff concrete mixture generally designed with a zero-slump value and compacted with a vibratory roller. It is commonly used in pavement construction. To reduce the utilization of cement, this study employs fly ash at variations of 0%, 40%, and 50% as cement replacements to study fresh concrete’s workability and the hardened concrete’s mechanical properties. The workability of fresh concrete coming from the vebe test result shows that all the mixtures, according to Brownsville TX, meet the workability criteria as RCC. Moreover, it is concluded that using fly ash as a partial replacement for cement has a positive impact on the compressive strength and splitting tensile strength of concrete. Full article

The present study investigates the effects of different compaction methods on the properties of roller-compacted concrete (RCC) used for road pavements. The study focuses on comparing the Proctor compaction method utilizing different compaction efforts and molds (2.5 kg rammer with three layers of 56 blows and 4.5 kg with three and five layers of 56 blows, cylindrical and cube molds) with a slab compactor in static and vibratory setting. The samples produced in a slab compactor were obtained by drilling from the prepared slab. The evaluated properties of the samples included compressive strength and bulk density. The study involved a C25/30 concrete with the intention to be used in low volume roads according to national standards. The study concluded that the utilization of Proctor compaction and slab compactor with vibratory setting provided similar levels of strength performance of the RCC mixture, regardless of the shape of the Proctor compacted samples. In terms of the bulk densities, the main differentiating factor in the case of Proctor compaction was the weight of the rammer. The compressive strength of the samples was also strongly related to their bulk densities. Full article

In this paper, the early drying shrinkage coefficients of different hydraulic cement mortars are calibrated through laboratory experiments for moderate-heat Portland cement (MHPC) and low-heat Portland cement (LHPC). By developing an improved mesoscale modeling approach, a 3D highly detailed simulation of concrete was generated, which incorporates the phases of mortar, aggregates, and interfacial transition zone (ITZ). The simulation result is in good agreement with the concrete early drying shrinkage experiment, exhibiting an error of less than 4.99% after 28 days. Subsequently, the mesoscale model is employed to explain the influence of the ambient humidity, cement type, and aggregate volume ratio on the early drying shrinkage performance of concrete. The results show that the early drying shrinkage coefficient of the LHPC is approximately 82% of the MHPC. Additionally, the depth of ambient humidity influence is about 15 mm from the concrete surface after 28 days. The early drying shrinkage can be controlled by increasing ambient humidity via the LHPC or raising the aggregate volume ratio. The mass-loss rate of concrete decreases as the ambient humidity or aggregate volume ratio increases during the process of drying shrinkage. Furthermore, the results quantify the influence patterns of various factors on drying shrinkage, thereby facilitating their application in assessing the cracking time induced by early drying shrinkage in roller-compacted concrete (RCC) dams. This provides theoretical guidance for crack prevention in concrete structures and aids in developing strategies for the construction of crack-free dams. Full article

Cemented Sand, Gravel, and Rock (CSGR) dams have traditionally used either Conventional Vibrated Concrete (CVC) or Grout-Enriched Roller Compacted Concrete (GERCC) for protective and seepage control layers in low- to medium-height dams. However, these methods are complex, prone to interference, and uneconomical due to significant differences in the expansion coefficient, elastic modulus, and hydration heat parameters among CSGR, CVC, and GERCC. This complexity complicates quality control during construction, leading to the development of Grout-Enriched Vibrated Cemented Sand, Gravel, and Rock (GECSGR) as an alternative. Despite its potential, GECSGR has limited use due to concerns about freeze–thaw resistance. This project addresses these concerns by developing an air-entrained GECSGR grout formulation and construction technique. The study follows a five-phase approach: mix proportioning of C₁₈₀6 CSGR; optimization of the grout formulation; determination of grout addition rate; evaluation of small-scale lab samples of GECSGR; and field application. The results indicate that combining 8–12% of 223 kg/m³ cement grout with 2–2.23 kg/m³ of admixtures, mud content of 15%, a marsh time of 26–31 s. and a water/cement ratio of 0.5–0.6 with the C₁₈₀6 parent CSGR mixture achieved a post-vibration in situ air content of 4–6%, excellent freeze–thaw resistance (F300: mass loss <5% or initial dynamic modulus ≥60%), and permeability resistance (W12: permeability coefficient of 0.13 × 10⁻¹⁰ m/s). The development of a 2-in-1 slurry addition and vibration equipment eliminated performance risks and enhanced efficiency in field applications, such as the conversion of the C₁₈₀4 CSGR mixture into air-entrained GECSGR grade C9015W6F50 for the 2.76 km Qianwei protection dam. Economic analysis revealed that the unit cost of GECSGR production is 18.3% and 6.33% less than CVC and GERCC, respectively, marking a significant advancement in sustainable cement-based composite materials in the dam industry. Full article

On 6 February 2023, two major earthquakes struck Türkiye, with their epicenters in the Pazarcık (M7.7; focal depth: 8.6 km) and Elbistan (M7.6; focal depth: 7 km) districts of Kahramanmaraş city. Most of the dams in the earthquake region remained structurally safe and stable. However, 17 dams in Türkiye and 1 dam in Syria were damaged during the 2023 Kahramanmaraş earthquakes. The main objective of this study was to better understand the real seismic behaviors of the dams during the two mainshocks and significant aftershocks. An earthfill dam, a concrete-faced rockfill dam (CFRD), and a roller-compacted concrete (RCC) dam constructed in the disaster area were selected to identify the real seismic behaviors of different types of dams during strong earthquakes. Acceleration records measured at the crest, right and left abutments, and foundations of the selected dams during the 2023 Kahramanmaraş earthquakes were taken into account to determine the real seismic behavior of the dams before, during, and after the earthquakes. The results of this investigation provide valuable insights into the real seismic behaviors of different types of dams in the vicinity of fault lines during strong earthquakes. Full article

In recent years, the use of recycled aggregate (RA) in roller-compacted concrete (RCC) for pavement construction has been increasingly attractive due to various environmental and economic benefits. Early determination of the compressive strength (CS) is crucial for the construction and maintenance of pavement. This paper presents the idea of combining metaheuristics and an advanced gradient boosting regressor for estimating the compressive strength of roller-compacted concrete containing RA. A dataset, including 270 samples, has been collected from previous experimental works. Recycled aggregates of construction demolition waste, reclaimed asphalt pavement, and industrial slag waste are considered in this dataset. The extreme gradient boosting machine (XGBoost) is employed to generalize a functional mapping between the CS and its influencing factors. A recently proposed gradient-based optimizer (GBO) is used to fine-tune the training phase of XGBoost in a data-driven manner. Experimental results show that the hybrid GBO-XGBoost model achieves outstanding prediction accuracy with a root mean square error of 2.64 and a mean absolute percentage error less than 8%. The proposed method is capable of explaining up to 94% of the variation in the CS. Additionally, an asymmetric loss function is implemented with GBO-XGBoost to mitigate the overestimation of CS values. It was found that the proposed model trained with the asymmetric loss function helped reduce overestimated cases by 17%. Hence, the newly developed GBO-XGBoost can be a robust and reliable approach for predicting the CS of RCC using RA. Full article

The addition of macro fibers to concrete pavements has been used to improve the cracking of concrete pavement, reduce slab thickness and contribute to increasing the joint spacing. A laboratory test was carried out in the study to analyze the impact of fiber reinforced concrete (FRC) on plain cement concrete (PCC) and roller compacted concrete (RCC), determining the flexural strength by performing ASTM-1609 tests and compressive strength by ASTM C-39 tests. Two synthetic fiber types selected with different geometries and different dosages (0.25% and 0.5% by volume) were tested for both RCC and PCC. To examine the effect of fiber contents and property, statistical testing was done using strength-test data. The test result showed that flexural strength was not affected by fibers. As fiber content increased, both residual strength (F₆₀₀ and F₁₅₀) and specimen toughness (T₁₅₀) increased for each fiber type. To the contrary, the compressive strength of specimens with higher fiber contents was lower in every case. Fiber properties including length and shape affected the residual strength of RCC more, than PCC. It is notable that the residual strength of RCC and PCC with the same fiber condition is very similar, even though the mix design and compressive and flexural strengths are different. In this paper, the strength-test data results are discussed, and the factors affecting the test results and the limitations of the testing methods are suggested. Full article

The widespread adoption of high concrete gravity dams in China and globally underscores the necessity for enhancing design processes to address potential risks, notably hydraulic fracture. This study delves into this urgency by scrutinizing common design regulations and investigating the impact of hydraulic fracture on high concrete gravity dams. A comparative analysis of design specifications from China, the USA, and Switzerland, employing the gravity method, elucidates distinctions, focusing on the Guxian dam. In addition, evaluation of standards with higher resistance to hydraulic fracture was conducted using the Finite Element Method (FEM) with XFEM (eXtended Finite Element Method), employing initial cracks with different depths at the dam heel ranging from 0.2 to 2 m. The vulnerability of the Guxian dam’s cross-section to safety risks prompts further inquiry into the dam’s resistance to hydraulic fracture. Therefore, high-pressure water splitting risks to the ultimate bearing capacity were examined through FEM simulation and theoretical calculations. FEM simulations assessed the dam’s ultimate bearing capacity with and without automatic crack propagation combining the XFEM and overloading methods, particularly considering weak layers in the RCC (Roller-Compacted Concrete) dams. Theoretical calculations utilized a fracture mechanical evaluation model. This model derived mechanism formulas to assess the dam’s resistance to hydraulic fracture. Additionally, the investigation explored the effect of the uplift pressure on the ultimate overload coefficient. Findings indicated that the Guxian dam’s current cross-sectional area was insufficiently safe against hydraulic fracture, necessitating an increase to its cross-sectional area to 18,888.1 m². Notably, the USA’s and Switzerland’s criteria exhibited greater resistance to hydraulic fracture than the Chinese criteria, especially without considering uplift pressure. Also, the Chinese regulations tended to calculate a lower dam cross-sectional area compared with the other regulations. Numerical calculations revealed a substantial decrease in overall dam safety (up to 48%) when considering automatic crack propagation and the dam’s weak layers. The fracture mechanical evaluation model showed that the Guxian dam had the lowest resistance, with an overloading coefficient of 1.05 considering the uplift pressure. In the case of not considering the uplift pressure, the dam resistance to hydraulic fracture increased and the overloading coefficient rose to 1.27. The results highlighted the risk of hydraulic fracture in concrete dams. Hence, it is recommended that design specifications of high concrete gravity dams incorporate safety analyses of hydraulic fracture in the design process. Reducing uplift pressure plays a crucial role in enhancing the dam’s resistance to hydraulic fractures, emphasizing the need for this consideration in safety evaluations. The differences between the three design specifications were particularly pronounced for dams higher than 200 m. In contrast, dams of 50 m yielded similar results across these regulations. Full article

Effective seepage control is crucial for maintaining the structural integrity of Cemented Sand, Gravel and Rock (CSGR) dams. Traditional methods using conventional concrete (CVC) or grout-enriched roller-compacted concrete (GERCC) are costly and disruptive. This paper presents a novel technique for constructing the protection and seepage control layer in Cemented Sand, Gravel and Rock (CSGR) dams. The method involves grouting and vibrating the loosened Cemented Sand, Gravel and Rock (CSGR) material to create vibrated grout-enriched Cemented Sand, Gravel and Rock, which performs similarly to concrete. A new surface water stop structure has also been developed for the structural joints. Laboratory tests revealed that Cemented Sand, Gravel and Rock (CSGR) with a vibrating–compacted (VC) value of 2–6 s and a compressive strength of 4 MPa meets design requirements for medium and low dams when the slurry addition rate is 8–12%. The T-shaped surface water stop demonstrated a bonding strength of over 1.8 MPa, withstanding a water pressure of 1.6 MPa. This method, integrated with dam body construction, reduces material costs by about 50% and eliminates construction interference. Specialized equipment for this technique has been developed, with a capacity of 12 m²/h. Implemented in the Minjiang Navigation and Hydropower Qianwei Project and Shaping I Hydropower Station, it has shown significant economic, environmental and safety benefits, promoting sustainable dam construction. Full article

In road engineering, road construction requires a large amount of natural aggregate; its substitution with recycled construction-solid-waste aggregate not only saves resources but also reduces the burden on the environment. The main components of construction solid waste are concrete blocks and brick slag; the breakability of the latter can affect the performance of mixed recycled aggregate, which hinders the use of construction solid waste in road engineering applications. To analyze the applicability of recycled construction-solid-waste aggregate containing brick slag aggregate in the subgrade layer, the effect of brick aggregate content on the CBR (California bearing ratio) and crushing value of mixed recycled aggregates was evaluated based on laboratory tests, and the field compaction quality of the recycled aggregates was analyzed. The results show that the 9.5–19 mm mixed recycled aggregate samples were crushed to a higher degree during the compaction process. A brick aggregate content less than 40% had little effect on the performance of mixed recycled construction-solid-waste aggregate. It is recommended to use a 22 t road roller for five passes (two weak vibrations + two strong vibrations + one weak vibration) at a speed of 3 km/h in the main compaction stage of the subgrade filling. Full article

Roller-compacted concrete (RCC) pavements have been the subject of studies focused on their increasing deterioration over time due to the influence of vehicular loading and ambient factors in humidity and temperature conditions ranging from medium to low (40% relative humidity and 25 °C temperature). Therefore, it is necessary to understand how they behave under various relative humidity and temperature conditions since these parameters vary in each geographic region. In this context, this research focused on analyzing the effect of drying shrinkage on RCC pavements under the influence of vehicular loading using a computational model calibrated with data obtained under typical ambient conditions. For this purpose, laboratory experiments were performed, numerical modeling was used, and the results for RCC pavements were validated using statistical analysis. The results revealed validated models providing moisture content and drying shrinkage curves. These results also underline the importance of considering ambient effects when calculating pavement stresses as a response variable in structural designs. In particular, these effects are highlighted as they can generate changes in pavement stresses of up to 10%, emphasizing the relevance of the models proposed in this study as they consider this phenomenon when predicting the performance and durability of RCC pavements. Full article

This research focuses on the behavior of roller-compacted concrete (RCC) used in pavements, which are prone to deterioration affecting their performance. These deteriorations result from various causes, including traffic load, errors during construction, mix design, and ambient conditions. Among these, ambient conditions could lead to a marked variable impact on material behavior and durability depending on the conditions associated with each region. Accordingly, this study aims to deepen the understanding of the effect, which a broader range of ambient conditions and different mix designs have on the physical and mechanical properties of RCC. Measurements such as the amount of water vapor per kilogram of air were used to apply the findings comprehensively. The RCC analysis encompassed experimentation with different compositions, altering the cement water ratio amount, and adding a superplasticizer. The impact of curing on the materials was evaluated before subjecting them to various humidity and temperature conditions. Laboratory tests were conducted to measure performance, including moisture, shrinkage, compressive strength, and the progression of flexural fracture resistance over curing periods of up to 90 days. The results revealed a logarithmic correlation between shrinkage and ambient humidity, which is the most determining factor in performance. Mix optimization through increased cement and reduced water enhanced the tensile strength of the material. Furthermore, the curing process was confirmed to increase resistance to shrinkage, especially in the long term, establishing it as a crucial element for the structural stability of RCC, which is relatively insensitive to variations in ambient conditions. Full article