The growing demand for sustainable construction materials has intensified interest in the use of natural fibers as reinforcement in concrete. This study presents a critical review of recent research on natural fiber–reinforced concrete (NFRC), with particular emphasis on abaca, bamboo, banana, coconut coir, and jute fibers. The review synthesizes experimental findings on the effects of these fibers on the physical, mechanical, and selected durability-related properties of concrete. Results from the literature indicate that natural fibers can significantly enhance tensile strength, flexural strength, toughness, ductility, and post-cracking behavior of concrete when incorporated at optimal dosages, typically at low volume fractions. Fibers such as abaca and jute show notable improvements in strength characteristics, while banana and coconut coir fibers primarily contribute to increased energy absorption and impact resistance. However, reductions in workability and inconsistent compressive strength performance are commonly reported, due to the hydrophilic nature, variability, and dispersion challenges of natural fibers. The review also highlights gaps in current research, particularly concerning long-term durability, fiber degradation in alkaline environments, and standardized mix design methodologies. Overall, the findings demonstrate that natural fibers offer a viable and environmentally friendly alternative to synthetic and steel fibers for selected structural and non-structural applications. Their use supports sustainability goals by reducing cement consumption, utilizing agricultural waste, and lowering the environmental footprint of concrete, while emphasizing the need for further research to enable wider engineering implementation.

Arsenic contamination in groundwater poses a persistent challenge in many urbanizing regions of the Philippines, particularly in Cavite, where mixed volcanic and carbonate aquifers are under increasing anthropogenic and geochemical stress. This study applies a quantitative geochemical simulation to evaluate the effects of pH, redox potential (Eh), and carbonate chemistry on arsenic speciation and mobility in Cavite groundwater. Using thermodynamic equilibrium modeling (PHREEQC) combined with logistic and adsorption-based parameterization, arsenite [As(III)] and arsenate [As(V)] species were simulated under Eh values 100–500 mV, pH 6.0–9.0, and total inorganic carbon (TIC) 1–10 mM. Results indicate that oxidizing conditions (Eh ≥ 300 mV) promote conversion of As(III) to As(V), while reducing conditions favor As(III), the more toxic and mobile form. The speciation transition between H2AsO4− and HAsO42− occurs near pH 6.9, consistent with experimental pKa values. Increasing carbonate concentrations significantly reduce arsenic adsorption, raising dissolved As from ≈17 μg/L to ≈30 μg/L. These patterns align with local hydrochemical observations in Cavite and comparable tropical aquifer systems. The integrated modeling framework highlights the coupled control of redox, pH, and carbonate equilibria on arsenic behavior in groundwater. The study provides a mechanistic basis for assessing arsenic transport and supports sustainable groundwater management and remediation strategies for Cavite and similar hydrogeologic settings.

Seepage is a critical factor influencing the stability of earth dams, as uncontrolled seepage can result in internal erosion, piping, and structural failure. This paper proposes assessing how effective a filter drain is in reducing the exit gradient and managing seepage near the downstream slope of a homogenous earth dam. The study utilizes SEEP/W software for modeling and analyzing seepage dynamics in a homogenous and isotropic earth dam. The results indicate that without a filter drain, seepage flow is directed toward the toe of the dam, a particularly vulnerable point where structural collapse or damage is most likely to occur. However, with the installation of a filter drain, the seepage flow direction and the phreatic line are shifted away from the toe, thereby reducing the risk of instability. The findings also reveal that variations in the length of the filter drain influence the exit gradient, while the assumed permeability values have a minimal impact on the exit gradient. These results provide valuable insights into optimizing filter drain design for improving the stability and safety of earth dams.