Suctions, fracture energy, and plastic cracking of cement mortar and concrete

Plastic cracking of cement mortar and concrete is primarily attributable to desiccation by evaporation from unprotected surfaces. This causes high suctions (negative pressures) to develop in the pore water adjacent to these surfaces. Dissolved salts in the pore water can also contribute significantly to suctions. Quantitative expressions are available for all of the components of the total suction. The development of suctions over time is illustrated by the results of desiccation tests conducted on cement mortars, supplemented by data from the literature. It is shown that ambient conditions conducive to plastic cracking can arise almost anywhere, but that the extremely high suctions that develop in mature cement mortar and concrete do not imply that compression failures should occur A high value of fracture energy is derived from data from the desiccation tests that implies that plastic cracking is characterized by a significant zone of plastic straining or microcracking.

Crack depths in desiccating plastic concrete

The depths of cracks in desiccating plastic concrete are estimated by considering the effects of the suction (negative pore pressure) associated with desiccation and applying five failure models derived from fracture, theories combined with theories drawn from geotechnical engineering under the assumption that plastic concrete is a frictional particulate material. The estimated crack depths vary with the depth of desiccation, the suction profile, and a small number of material parameters that depend on the model adopted and are comparatively easy to estimate accurately. Four of the models predict excessively large crack depths. The fifth, however, predicts shallower crack depths that increase with the age of the concrete and are consistent with those of analogous desiccation cracks in coal mine tailings. It thus offers a relatively robust method of estimating the depth of desiccation cracks. Confirmation of this with data for plastic concrete is clearly desirable but not possible at present.

The effect of organic mulch amendments on the physical and chemical properties and revegetation success of a saline-sodic minespoil from central Queensland, Australia

Saline-sodic clay minespoil materials excavated during open-cut coal mining in central Queensland, Australia, pose significant challenges for revegetation, particularly where suitable topsoil capping is not available. We examined the ability of sawdust or straw mulch amendments to ameliorate the adverse properties of these minespoils and improve the success of revegetation efforts. In laboratory studies, mulch application improved infiltration, increased soil moisture retention and reduced surface crust strength. In the field, mulches incorporated to a depth of 0.15 m at application rates of at least 20 t/ha straw or 80 t/ha sawdust were needed to mitigate against capillary rise of salts during drying cycles and support satisfactory vegetation cover. Further research is needed to determine whether improvements are maintained beyond the 4-year trial period reported here.

Highly thermally responsive hybrid in-fiber slab waveguide grating structure with a plastic core and a silica cladding

A 1.2(height)×125(depth)×500(length) micro-slot was engraved along a fiber Bragg grating by chemically assisted femtosecond laser processing. By filling epoxy and UV-curing, waveguide with plastic-core and silica-cladding was created, presenting high thermal responding coefficient of 211pm/°C.

Highly thermally responsive hybrid in-fiber sSlab waveguide grating structure with a plastic core and a silica cladding

A 1.2(height)×125(depth)×500(length) micro-slot was engraved along a fiber Bragg grating by chemically assisted femtosecond laser processing. By filling epoxy and UV-curing, waveguide with plastic-core and silica-cladding was created, presenting high thermal responding coefficient of 211pm/°C.