A clonal selection algorithm model for daily rainfall data prediction.

This study applies the clonal selection algorithm (CSA) in an artificial immune system (AIS) as an alternative method to predicting future rainfall data. The stochastic and the artificial neural network techniques are commonly used in hydrology. However, in this study a novel technique for forecasting rainfall was established. Results from this study have proven that the theory of biological immune systems could be technically applied to time series data. Biological immune systems are nonlinear and chaotic in nature similar to the daily rainfall data. This study discovered that the proposed CSA was able to predict the daily rainfall data with an accuracy of 90% during the model training stage. In the testing stage, the results showed that an accuracy between the actual and the generated data was within the range of 75 to 92%. Thus, the CSA approach shows a new method in rainfall data prediction.

Evaluation of the Superiority of Lightweight-Aggregate-Concrete Prestressed Box Girders in Terms of Durability and Prestress Loss.

This case study aimed to compare the differences in the durability and prestress loss between normal-weight-concrete (NC) and lightweight-aggregate-concrete (LWC) prestressed box girders, which were constructed at the same time in the same area, so as to verify the superiority of using synthetic lightweight aggregate (LWA) made from reservoir sediments in prestressed bridges. For the NCs and LWCs used in the prestressed box girders, the basic mechanical properties (compressive strength, flexural strength, splitting tensile strength, and elastic modulus) were tested, as well as the durability properties (chloride ion penetration resistance and rapid chloride permeability). Then, through the prestress-monitoring system, the prestress losses of the two groups of prestressed box girders were tracked. The results of the durability test confirmed that LWC can inhibit the penetration of air, water, and chloride ions by strengthening the interfacial transition zone between the aggregate and the cement paste, thereby improving its durability. Moreover, the magnetic-flux prestress loss of the NC prestressed box girder reached 8.1%. In contrast, the magnetic-flux prestress losses on both sides of the LWC prestressed box girder were 4.6% and 4.9%, respectively. This verified that, under the same environmental conditions, the use of LWC produced less of a prestress loss than the use of NC.

The Evaluation of the Effectiveness of Biomineralization Technology in Improving the Strength of Damaged Fiber-Reinforced LWAC.

Concrete cracks and local damage can affect the bond performance between concrete and steel bars, thereby reducing the durability of reinforced concrete structures. Compared with general concrete crack repair methods, biomineralization repair not only has effective bonding capabilities but is also particularly environmentally friendly. Therefore, this study aimed to apply biomineralization technology to repair damaged fiber-reinforced lightweight aggregate concrete (LWAC). Two groups of LWAC specimens were prepared. The experimental group used lightweight aggregates (LWAs) containing bacterial spores and nutrient sources, while the control group used LWAs without bacterial spores and nutrient sources. These specimens were first subjected to compression tests and pull-out tests, respectively, and thus were damaged. After the damaged specimen healed itself in different ways for 28 days, secondary compression and pull-out tests were conducted. The self-healing method of the control group involved placing the specimens in an incubator. The experimental group was divided into experimental group I and experimental group II according to the self-healing method. The self-healing method of experimental group I was the same as that of the control group. The self-healing method of experimental group II involved soaking the specimen in a mixed solution of urea and calcium acetate for two days, and then taking it out and placing it in an incubator for two days, with a cycle of four days. The test results show that in terms of the relative bond strength ratio, the experimental group II increased by 17.9% compared with the control group. Moreover, the precipitate formed at the cracks in the sample was confirmed to be calcium carbonate with the EDS and XRD analysis results, which improved the compressive strength and bond strength after self-healing. This indicates that the biomineralization self-healing method used in experimental group II is more effective.

Sustainable Use of Sludge from Industrial Park Wastewater Treatment Plants in Manufacturing Lightweight Aggregates.

The aim of this study was to investigate the development of a process for manufacturing lightweight aggregates (LWAs) by incorporating sludge from wastewater treatment plants in industrial parks with reservoir sediments. The research was divided into two stages: laboratory-scale firing and large-scale firing. In the laboratory-scale stage, a high-temperature furnace was used for trial firing. In the large-scale stage, a commercial rotary kiln was used for trial firing for mass production. The test results showed that the water absorption, dry loose bulk density, and crushing strength of the sintered LWAs were 14.2-26.9%, 634-753 kg/m3, and 1.29-2.90 MPa, respectively. Moreover, the water absorption of the sintered LWAs increased as the percentage of added sludge increased. In addition, the dry loose bulk density of the sintered LWAs gradually decreased as the percentage of added sludge increased. Moreover, the results of the heavy metal toxicity characteristic leaching procedure (TCLP) dissolution test for the LWAs produced by blending 30-50% sludge were all lower than the standard value required by the Taiwan Environmental Protection Agency for general industrial waste. The strength grade of the sintered LWAs was 20 MPa. From this point of view, the sintered LWAs that were studied under the test conditions could be used as aggregates for lightweight concrete and would allow it to have a reasonable strength of greater than 20 MPa.

The Corrosion Resistance of Reinforced Lightweight Aggregate Concrete in Strong Brine Environments.

Taiwan has used technology in reservoir sediments and industrial waste to produce high-performance lightweight aggregate (LWA). LWA can be used to manufacture lightweight aggregate concrete (LWAC) with structural strength ratings. At present, Taiwan's offshore wind turbines are gradually developing and are moving from coastal areas to deep-sea areas. With this in mind, this study aimed to investigate the feasibility of applying LWAC with synthetic LWA from reservoir sediments to floating offshore wind turbine foundations. LWAC and normal-weight concretes (NWC) of different strengths were prepared, and their fresh, hardened, and durability properties were tested. In addition, reinforced concrete and steel sheets were immersed in a tank of high salinity seawater to examine their resistance to seawater-accelerated corrosion. The test results showed that the total passing charge of the two groups of concrete within six hours was less than 1000 coulombs. Both groups of concrete were classified as having "Very Low" chloride permeability. The average corrosion potential of most reinforced concrete specimens was found to be greater than -200 mV, which means that the corrosion probability of the steel bars was less than 10%. Furthermore, the use of coatings for seawater corrosion protection on steel sheets was not found to be as effective as reinforced concrete. This shows that the use of LWAC with synthetic LWA from reservoir sediments for the floating foundations of offshore wind turbines is feasible and has design flexibility.

Application of Biomineralization Technology to Self-Healing of Fiber-Reinforced Lightweight Concrete after Exposure to High Temperatures.

In the field of civil engineering, concrete self-healing technology plays an important role. Concrete self-healing should be able to effectively heal cracks, not only improving the internal structure, but also improving the mechanical properties and durability of the concrete structure. The biomineralization-repair method is characterized by its potential for long-lasting, rapid, and active crack repair potential. Biomineralization repair has an effective bond ability, is compatible with concrete components, and is also environmentally friendly. This study used biomineralization to explore the self-healing of fiber-reinforced lightweight concrete after its exposure to high temperatures. Concrete specimens of a control group (using lightweight aggregate without bacterial spores and a nutrient source) and an experimental group (using lightweight aggregate containing bacterial spores and a nutrient source) were prepared. The repair effect of the microbial self-healing concrete after the exposure to high temperature was observed by a crack-width gauge, field-emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). According to the EDS and XRD analyses, the precipitate formed at the crack was calcium carbonate. After 28 days of self-healing, the water absorption rate of the experimental group was lower than that of the control group. This is because the specimens of the penetration test were taken from the middle of the concrete cylinder after high temperature, and their bacterial survival rate was higher, which made the mineralization more significant. However, the mechanical test results of the control and experimental groups after the self-healing in the water were not substantially different, which indicated that the bacterial mineralization in the experimental group was slow in the absence of an adequate source of nutrients.

Modeling Uniaxial Bond Stress-Slip Behavior of Reinforcing Bars Embedded in Concrete with Different Strengths.

This paper aims to study the uniaxial bond stress-slip characteristics of reinforcing bars embedded in concrete with different strengths. Tests were conducted on tension-pull specimens that had a cross-sectional dimension with a reinforcing bar embedded in the center section. The experimental variable was the concrete compressive strength (20, 40, and 60 MPa). The test results show that in the specimen subjected to any fixed load, the maximum value of the concrete strain occurred around the central position, and its value increased as the compressive strength of the concrete increased. Depending on the embedded position of the steel bars, the bond stress-slip relationship was also different. In addition, the analytical results indicate that the proposed bond stress-slip constitutive relationship is very accurate in describing the true bond stress-slip relationship.

Flexural Behavior of Ultra-High-Performance Fiber-Reinforced Concrete Beams after Exposure to High Temperatures.

Due to the dense structure of ultra-high-performance concrete (UHPC), it is prone to explosive spalling at high temperatures. In this paper, flexural testing of UHPC and high-strength concrete (HSC) beams was carried out at room temperature and after being subjected to different levels of thermal exposure (300-500 °C). The cross-section of the beam specimen was 150 (width) × 200 (depth) mm, and its length was 1500 mm. The flexural and shear design of the beam specimens were carried out in accordance with the ACI 318M-14 code. All of the beams were singly reinforced with two #4 rebars (minimum reinforcement ratio) as a longitudinal tensile reinforcement at the bottom of the specimen and at an effective depth of 165 mm. The flexural load was applied using the three-point load method. The results show that, at room temperature and after being subjected to different thermal exposures, compared with the HSC specimens, the stiffness of the UHPC specimens in the post-cracking stage was relatively larger and the deflection under a given load was smaller. Moreover, whether at room temperature or after exposure to different thermal exposures, the ductility of the UHPC specimens was better than that of the HSC specimens.

Modeling Local Bond Stress-Slip Relationships of Reinforcing Bars Embedded in Concrete with Different Strengths.

Although many different analytical models of local bond stress-slip have been proposed, considering the possible differences between materials in different countries, their applicability needs to be further explored. In this paper, the local bond stress-slip characteristics of reinforcing bars embedded in concrete with different strengths were experimentally studied. The experimental variables included the concrete strength (20, 40, and 60 MPa) and deformed rebar size (#4, #6, and #8). The experimental results of the bond stress-slip relationship were compared with the Euro-International Concrete Committee (CEB-Comité Euro-International du Béton)-International Federation for Prestressing (FIP-Fédération Internationale de la Précontrainte) Model Code and prediction models found in the literature. In addition, based on the test results, an empirical model of the bond stress-slip relationship was proposed. The evaluation and comparison results show that, regardless of the concrete strength grades, the predicted value calculated using the CEB-FIP Model Code will underestimate the bond strength of the specimens with different steel bar diameters. From this perspective, it is more conservative. In contrast, the proposed model can predict the test results with a reasonable accuracy.

Mechanical Properties of Ultra-High Performance Concrete before and after Exposure to High Temperatures.

Compared with ordinary concrete, ultra-high performance concrete (UHPC) has excellent toughness and better impact resistance. Under high temperatures, the microstructure and mechanical properties of UHPC may seriously deteriorate. As such, we first explored the properties of UHPC with a designed 28-day compressive strength of 120 MPa or higher in the fresh mix phase, and measured its hardened mechanical properties at seven days. The test variables included: the type of cementing material and the mixing ratio (silica ash, ultra-fine silicon powder), the type of fiber (steel fiber, polypropylene fiber), and the fiber content (volume percentage). In addition to the UHPC of the experimental group, pure concrete was used as the control group in the experiment; no fiber or supplementary cementitious materials (silica ash, ultra-fine silicon powder) were added to enable comparison and discussion and analysis. Then, the UHPC-1 specimens of the experimental group were selected for further compressive, flexural, and splitting strength tests and SEM observations after exposure to different target temperatures in an electric furnace. The test results show that at room temperature, the 56-day compressive strength of the UHPC-1 mix was 155.8 MPa, which is higher than the >150 MPa general compressive strength requirement for ultra-high-performance concrete. The residual compressive strength, flexural strength, and splitting strength of the UHPC-1 specimen after exposure to 300, 400, and 500 °C did not decrease significantly, and even increased due to the drying effect of heating. However, when the temperature was 600 °C, spalling occurred, so the residual mechanical strength rapidly declined. SEM observations confirmed that polypropylene fibers melted at high temperatures, thereby forming other channels that helped to reduce the internal vapor pressure of the UHPC and maintain a certain residual strength.

Mix Design and Mechanical Properties of High-Performance Pervious Concrete.

The mechanical properties of traditional pervious concrete are insufficient, which limits its application. In view of the imperfections of traditional permeable concrete in mechanics, this paper aimed to find a suitable material composition that can be used as a feasible mix design of high-performance pervious concrete, to essentially improve its mechanical properties. Based on the view that concrete is a two-phase material, in order to understand the rheological properties of the matrix, it was subjected to a rheological test, and then the filler aggregate was uniformly incorporated into the aforementioned matrix to further explore the composition and properties of the resulting pervious concrete. For the matrix, the orthogonal array employed was L16(45), which consisted of five factors, each with four levels. Base on the fluidity and compressive strength of the tested matrix, three groups of suitable matrixes mix proportions were selected to serve as the matrix type for pervious concrete mix proportion design. Then, an orthogonal array L9(34), which consisted of four controllable three-level factors, was adopted in the pervious concrete. The parameters investigated included the coarse aggregate size, fine aggregate content, matrix type, and aggregate-to-binder ratio. The test results demonstrate that the key factors affecting the compressive strength of the matrix and the pervious concrete were closely related to the cementitious material. In the matrix, the proportion of the cementitious material was the most important factor, while in the pervious concrete, the type of matrix was the most important factor.

Self-Healing Concrete by Biological Substrate.

At present, the commonly used repair materials for concrete cracks mainly include epoxy systems and acrylic resins, which are all environmentally unfriendly materials, and the difference in drying shrinkage and thermal expansion often causes delamination or cracking between the original concrete matrix and the repair material. This study aimed to explore the feasibility of using microbial techniques to repair concrete cracks. The bacteria used were environmentally friendly Bacillus pasteurii. In particular, the use of lightweight aggregates as bacterial carriers in concrete can increase the chance of bacterial survival. Once the external environment meets the growth conditions of the bacteria, the vitality of the strain can be restored. Such a system can greatly improve the feasibility and success rate of bacterial mineralization in concrete. The test project included the microscopic testing of concrete crack repair, mainly to understand the crack repair effect of lightweight aggregate concrete with implanted bacterial strains, and an XRD test to confirm that the repair material was produced by the bacteria. The results show that the implanted bacterial strains can undergo Microbiologically Induced Calcium Carbonate Precipitation (MICP) and can effectively fill the cracks caused by external concrete forces by calcium carbonate deposition. According to the results on the crack profile and crack thickness, the calcium carbonate precipitate produced by the action of Bacillus pasteurii is formed by the interface between the aggregate and the cement paste, and it spreads over the entire fracture surface and then accumulates to a certain thickness to form a crack repairing effect. The analysis results of the XRD test also clearly confirm that the white crystal formed in the concrete crack is calcium carbonate. From the above test results, it is indeed feasible to use Bacillus pasteurii in the self-healing of concrete cracks.

Application of the Taguchi Method for Optimizing the Process Parameters of Producing Lightweight Aggregates by Incorporating Tile Grinding Sludge with Reservoir Sediments.

This study aimed to apply the Taguchi optimization technique to determine the process conditions for producing synthetic lightweight aggregate (LWA) by incorporating tile grinding sludge powder with reservoir sediments. An orthogonal array L16(45) was adopted, which consisted of five controllable four-level factors (i.e., sludge content, preheat temperature, preheat time, sintering temperature, and sintering time). Moreover, the analysis of variance method was used to explore the effects of the experimental factors on the particle density, water absorption, bloating ratio, and loss on ignition of the produced LWA. Overall, the produced aggregates had particle densities ranging from 0.43 to 2.1 g/cm³ and water absorption ranging from 0.6% to 13.4%. These values are comparable to the requirements for ordinary and high-performance LWAs. The results indicated that it is considerably feasible to produce high-performance LWA by incorporating tile grinding sludge with reservoir sediments.

Paper Sludge Reuse in Lightweight Aggregates Manufacturing.

The lightweight aggregates used by the civil engineering market are sintered at a high temperature, about 1200 °C. In times of high energy prices and regulation of carbon dioxide emissions, lightweight aggregate products of the high-temperature process in sales marketing are not readily accepted. This study developed a sintered-type paper sludge lightweight aggregate. In order to reduce energy consumption, substitution of some reservoir sediment clay in paper sludge substitutes is to be expected. The study used two types of paper sludge (green clay paper sludge and paper pulp sludge). The sintering temperature was reduced effectively as the green clay paper sludge was substituted for some of the reservoir sediment clay, and the optimum substitute ranges of green clay paper sludge were 10%-50%. The optimum substitute ranges of the paper pulp sludge were 10%-40%. Test results show that the properties of aggregates have a particle density of 0.66-1.69 g/cm³, a water absorption of 5%-30%, and a loss on ignition of 10%-43%. The loss on ignition of aggregate became greater with the increase in paper sludge content. This means that the calorific value provided by the paper sludge will increase as paper sludge content increases. Paper sludge can therefore be considered a good material to provide heat energy for sintering lightweight aggregate.