Cracks in concrete generally interconnect flow paths and increase concrete permeability. The increase in concrete permeability due to the progression of cracks allows more water or aggressive chemical ions to penetrate into the concrete, facilitating deterioration. The present work studies the relationship between crack characteristics and concrete permeability. In this study, feedback controlled splitting tests are introduced to generate crack widthcontrolled concrete specimens. Sequential crack patterns with different crack widths are viewed under a microscope. The permeability of cracked concrete is evaluated by water permeability tests. The preliminary results indicate that crack openings generally accelerate water flow rate in concrete. When a specimen is loaded to have a crack opening displacement smaller than 50 microns prior to unloading, the crack opening has little effect on concrete permeability. When the crack opening displacement increases from 50 microns to about 200 microns, concrete permeability increases rapidly. After the crack opening displacement reaches 200 microns, the rate of water permeability increases steadily. The present research may provide insight into developing design criteria for a durable concrete and in predicting service life of a concrete structure.

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The emergence of soft robots has presented new challenges associated with controlling the underlying fluidics of such systems. Here, we introduce a strategy for additively manufacturing unified soft robots comprising fully integrated fluidic circuitry in a single print run via PolyJet three-dimensional (3D) printing. We explore the efficacy of this approach for soft robots designed to leverage novel 3D fluidic circuit elements—e.g., fluidic diodes, “normally closed” transistors, and “normally open” transistors with geometrically tunable pressure-gain functionalities—to operate in response to fluidic analogs of conventional electronic signals, including constant-flow [“direct current (DC)”], “alternating current (AC)”–inspired, and preprogrammed aperiodic (“variable current”) input conditions. By enabling fully integrated soft robotic entities (composed of soft actuators, fluidic circuitry, and body features) to be rapidly disseminated, modified on demand, and 3D-printed in a single run, the presented design and additive manufacturing strategy offers unique promise to catalyze new classes of soft robots.

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.

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