A Simplified Model for Shear Behavior of Mortar Using Biomimetic Carbonate Precipitation.

As a common molecule in biomineralization, L-aspartic acid (L-Asp) has been proven to be able to induce in vitro CaCO3 precipitation, but its application in sand reinforcement has never been studied. In this study, L-Asp was employed in sand reinforcement for the first time through the newly developed biomimetic carbonate precipitation (BCP) technique. Specimens with different number of BCP spray cycles were prepared, and a series of direct shear tests were conducted to investigate the impact of spray number on shear strength, critical displacement, and residual strength. Then a simplified power model for shear stress-displacement behavior was established and calibrated with the measured data. The results show that BCP can significantly improve the shear strength of sand. As the number of spray cycles increases, both the shear strength and residual strength increase, while the critical displacement decreases. Such variations can be described with two sigmoid models and a linear model, respectively. The simplified power model performs well in most cases, especially at higher spray numbers. This study is expected to provide a practical model for the shear behavior of BCP-treated mortar.

Spatial dependence and determinants of conservation easement adoptions in the United States.

A conservation easement is a market-based instrument for environmental protection. It has achieved rapid growth in the United States over the past few decades. As of 2015, 1.75% of the country's total land was placed under the restriction of conservation easements. In this study, spatial dependence in adopting conservation easements in the United States and the underlying determinants are examined through a spatial econometric model. The spatial panel data covers 50 individual states and six five-year intervals from 1990 to 2015. The findings reveal that spatial correlation in adopting conservation easements across individual states has become stronger over the study period, and the indirect spillover effect for most covariates is as high as one-third of the total effect. In addition, conservation easements have been utilized to protect threatened or strained natural resources. Populations with higher income or better education generally have helped the development of conservation easements. Government programs and policies favoring conservation easements also have positive impacts on easement adoption. These results can aid policymakers, landowners, and easement holders to efficiently allocate resources in acquiring conservation easements and managing currently eased land.