Biocement production from microbially induced calcium carbonate precipitation (MICP) is an environmentally friendly approach for construction works, but the use of calcium chloride (CaCl 2 ) in the conventional MICP process is a cost-limiting factor. The aim of this work is to develop a method for producing soluble calcium ions through two waste sources, limestone powder derived from aggregate quarries and acetic acid derived from fast pyrolysis of lignocellulosic biomass, as a replacement for the reagent grade CaCl 2 in the MICP process. The ratio of limestone powder to acetic acid solution was optimized for a desirable calcium concentration with an appropriate pH. Procedures for applying the urease-producing bacteria, urea, and calcium solutions were developed for a successful MICP process and were treated for sand column test. The engineering properties of the biocemented sand, including water permeability, unconfined compressive strength, and tensile strength, were evaluated as a function of the calcium carbonate content of the product. It was found that the properties of the sand treated using the limestone/acetic acid derived calcium solution were comparable to those of sand treated using reagent grade CaCl 2 . Collectively, the results indicate that the new MICP process is effective, more sustainable, and cheaper compared with the conventional MICP method.

Resistive random access memory based on the resistive switching phenomenon is emerging as a strong candidate for next generation non-volatile memory. So far, the resistive switching effect has been observed in many transition metal oxides, including strongly correlated ones, such as, cuprate superconductors, colossal magnetoresistant manganites and Mott insulators. However, up to now, no clear evidence of the possible relevance of strong correlation effects in the mechanism of resistive switching has been reported. Here, we study Pr0.7Ca0.3MnO3, which shows bipolar resistive switching. Performing micro-spectroscopic studies on its bare surface we are able to track the systematic electronic structure changes in both, the low and high resistance state. We find that a large change in the electronic conductance is due to field-induced oxygen vacancies, which drives a Mott metal-insulator transition at the surface. Our study demonstrates that strong correlation effects may be incorporated to the realm of the emerging oxide electronics.

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