Wave-dissipating Concrete Blocks Research Articles

Impact resistance of recycled-PET fiber strengthened wave-dissipating concrete block considering rocking motion

This study was conducted to enhance the impact resistance of wave-dissipating concrete blocks by recycled-Polyethylene Terephthalate (rPET) fibers. The aim of this study is to address the structural vulnerabilities of maritime structures and contribute to environmental issue. Traditionally, the stability of marine structures has been largely dependent on self-weight, a characteristic that can be undermined by damage from sea waves. Wave-dissipating concrete blocks are engineered to reduce the power of waves, but they remain susceptible to fractures caused by hoisting and rocking motions after installation. Existing evaluations often neglect the impact of rocking motion, primarily concentrating on fractures due to lifting. To enhance impact resistance, ultra-slow speed experimental tests were conducted to determine the fracture energy of concrete block considering rPET. The results revealed a significant improvement in the fracture energy of rPET reinforced concrete. Based on these experimental test results, a numerical model was developed to simulate the behavior of wave-dissipating concrete blocks considering rocking motion. The developed Smoothed Particle Hydrodynamics (SPH) model proved to be more relevant than the Finite Element (FE) model. Furthermore, this newly developed numerical model was utilized to evaluate structural performance. The results of the numerical analysis indicated a relationship between weight and impact velocity on the occurrence of damage. This led to the proposal of fragility curves for Sealock and TTP under various impact velocities during rocking motion. Fragility curves, developed based on impact velocity, demonstrated enhanced impact resistance of wave-dissipating concrete blocks reinforced with rPET. In addition, the incorporation of PET fibers effectively controlled crack propagation and improved impact resistance, particularly with increasing block weight. The methodology employed in this study holds potential for predicting outcomes using simple data, making it applicable to other scenarios such as vehicle-bridge pier collisions.

At the edge of the sea: the supralittoral nemertean, Acteonemertes orientalis sp. nov. (Nemertea: Eumonostilifera: Plectonemertidae) from Japan

Ribbon worms (phylum Nemertea) are found in oceans worldwide; however, only a few inhabit terrestrial, semiterrestrial and freshwater environments. In our study, we describe Acteonemertes orientalis sp. nov., a new species of Plectonemertidae Gibson, 1990 and the first plectonemertid discovered in Japan. The species was found in the supralittoral zone, from which nemerteans have rarely been reported and inhabits areas under rocks, wave-dissipating concrete blocks, and fallen leaves and stocks, along the coast of the Sea of Japan. Multi-locus phylogenetic analyses based on two mitochondrial (16S rRNA and cytochrome c oxidase subunit I) and two nuclear gene markers (18S rRNA and 28S rRNA) revealed that A. orientalis sp. nov. formed a clade with Leptonemertes cf. chalicophora collected from Florida. Although the external and internal morphology of A. orientalis sp. nov. is largely consistent with the generic diagnosis, this species differs in having a large proboscis. Based on the molecular and morphological data, we propose to amend the diagnosis of Acteonemertes by excluding proboscis size. ZooBank: urn:lsid:zoobank.org:pub:BBBE9549-5DCE-424F-9A39-930F8243C28B

Mechanical characterization of recycled-PET fiber reinforced mortar composites treated with nano-SiO2 and mixed with seawater

The study investigated the use of polyethylene terephthalate (rPET) fibers for strengthening construction materials. The addition of 0.5 vol% rPET fibers to mortar was studied, but the smooth surface of rPET resulted in weak bonds with the mortar matrix, leading to a decreased interfacial transfer zone (ITZ) compared to the surrounding matrix. To address this issue, nano-particle and NaOH hydrolysis were used to improve the ITZ bond strength and frictional behavior. Additionally, surface treatment of rPET using NaOH and silane coating was performed to enhance the hydrophilicity and bond strength with the matrix. The effects of seawater on the material were also studied using XRD. Additionally, cemGEMS analysis was also conducted. The SEM was used to observe the degree of bonding at the ITZ between rPET and the mortar matrix. The study showed that adding 0.5 vol% of rPET fibers had a significant impact on the tensile strength and fracture energy of mortar, and the fiber dispersibility was a crucial factor in controlling its mechanical properties. The low-cost recycled PET fibers were also found to be effective as a reinforcing agent in seawater-mixed mortar for marine applications, increasing the mortar's fracture energy by 188–802%. Therefore, these fibers can be used in coastal structures requiring impact-resistant non-metallic materials, such as wave-dissipating concrete blocks or marine concrete structures reinforced with non-corrosive materials like FRP.

STABILITY OF WAVE-DISSIPATING CONCRETE BLOCKS OF DETACHED BREAKWATERS AGAINST TSUNAMI

In recent years, the risk of occurrence of tsunamis generated by near shore earthquakes, such as, Tokai, Tonankai, Nankai and off-Miyagi is considered to be higher than before, as well as off shore tsunamis traveling long distances, e.g., the 2010 Chilean tsunami. On March, 11th, 2011 the huge, devastating tsunami generated by The 2011 off the Pacific coast of Tohoku Earthquake attacked and damaged the east coast area of Japan. Tsunami forces onto vertical walls, such as seawalls, has already been studied in detail, e.g., Asakura et al.(2002) and Kato et al.(2006). In Japan, detached breakwaters made with wave-dissipating concrete blocks such as Tetrapods have been widely applied. However, the effects of detached breakwater on tsunami disaster mitigation have not been studied. In our study, hydraulic model tests have been systematically and carefully carried out using solitary tsunami waves to evaluate the stability of concrete blocks following the our previous study on the effect of detached breakwaters from the viewpoint of reducing run-up and wave pressure onto seawalls behind the detached breakwaters (Hanzawa et al., 2011).

Applicability of CADMAS-SURF to evaluate detached breakwater effects on solitary tsunami wave reduction

Detached breakwaters, made with wave-dissipating concrete blocks such as Tetrapods, have been widely applied in Japan, but the effectiveness of such kinds of detached breakwaters on tsunami disaster prevention has never been discussed in detail. A numerical wave flume called CADMAS-SURF has been developed for advanced maritime structure design. CADMAS-SURF has been applied mainly to ordinary wave conditions such as wind waves, and little attempt has been made for expanding its application to tsunami waves. In this study, the applicability of CADMAS-SURF for evaluating the effectiveness of detached breakwaters on a solitary tsunami wave reduction is investigated by comparing the calculated results with those from hydraulic experiments. First, the effectiveness of a detached breakwater on the reduction of wave height and wave pressure was confirmed both by hydraulic experiments and numerical simulations. Finally, CADMAS-SURF has been found to be a useful tool for evaluating the effects of detached breakwaters on tsunami wave height and pressure reduction, as a first step in a challenging study.

Experimental Study on Stability of Wave-dissipating Concrete Blocks of Detached Breakwaters against Tsunami

In Japan, detached breakwaters made with wave dissipating concrete blocks such as Tetrapods have been widely applied. On March, 11th, 2011 the huge, devastating tsunami generated by The 2011 off the Pacific coast of Tohoku Earthquake attacked and damaged the east coast area of Japan. In our study, hydraulic model tests have been systematically and carefully carried out using solitary tsunami waves to evaluate the stability of concrete blocks following the our previous study on the effect of detached breakwaters from the viewpoint of reducing run-up and wave pressure onto seawalls behind the detached breakwaters.

A Study on Maintenance Methods Considering Expected Maintenance Costs of Caisson Breakwaters Covered with Wave-dissipating Concrete Blocks

In this study, we propose a new method for caisson breakwaters covered with wave-dissipation concrete blocks, which enables to evaluate cumulative maintenance costs including both ordinary maintenance costs (to raise work level of the blocks) and disaster recovery costs due to an extreme wave load. The method is based on a statistical model (Monte Carlo Simulation) calculating sliding distances of a caisson during its working life. This method can be effectively utilized for planning maintenance strategies, considering how the ordinary maintenance criteria for the settlement of the blocks affects the cumulative maintenance costs including information on both expected value and the its variations.

An Experimental Study on Deformation of Wave -Dissipating Concrete Blocks Covering Caisson Breakwaters

The purpose of this study is to investigate the deformation characteristics of wave-dissipating concrete blocks covering caisson breakwaters. Examples of actual deformation were examined to obtain knowledge on the features. The study suggested that the relative crown height of the breakwater affected the deformation of the wave-dissipating concrete blocks. A series of hydraulic stability tests was conducted to investigate the deformation characteristics. The test results show that deformation of wave-dissipating concrete blocks is different between low and high crown conditions.

Study on behaviors of wave-dissipating concrete blocks of submerged breakwater around the Fukui Port using GPS

Stabilization of the seawalls is required for protecting the important facilities along the coast of the Fukui Port. Since 2004, Ministry of Land, Infrastructure and Transport has commenced the projects for improvement of the existing seawalls for scouring and liquefaction protection, and for construction of new submerged breakwaters. Construction of “two-crested submerged breakwaters, ” which have two parallel crests along the coast, was newlycommenced in 2006. The ministry realized that stability of the submerged breakwater needs to be examined because the submerged breakwater experiences winter stormy waves while the construction of the breakwater is not yetcompleted, i. e., the total length of the breakwater is 45m compared to the designed total length of 200m. This paper presents a survey result of location of concrete armor blocks for the submerged breakwater on partial completion with using Real-Time-Kinematic GPS.

THE DEVELOPMENT OF A WAVE ABSORBING CAISSON BREAKWATER FOR ROUGH SEAS

In open sea region with severe wave attacks, a breakwater covered with wave-dissipating blocks have been widely used. However, the application of this breakwater at greater depths implies the increase of construction costs because it requires a large quantity of wave-dissipating concrete blocks. Therefore, the authors developed a new type of breakwater. This breakwaterconsists of wave absorbing caisson and sloping top caisson. In this paper, through the sliding experiment of this new type breakwater using a 1/60 model, we prove the stability and define the hydraulic characteristics of this breakwater.