Demolition Agents Research Articles

Temperature-related performance factors for chemical demolition agents

Soundless chemical demolition agents (SCDAs) are percussion-free alternatives to blasting for selective demolition. Although known to be temperature sensitive, to date their performance has not been quantified in ambient environments below 20°C. This paper examines 6 large-scale specimens at 16.1-19.3°C. Substantially slower response than that reported by manufacturers was documented. Initial cracking required 25 + h and continued for 4-8 days. Cracks opened rapidly after minimum demolition time [(MDT)-cumulative cracking around the perimeter reaching ~25 mm], which was at 42 and 70 h, respectively in 16.8 and 33.1 MPa specimens. Post-MDT, crack width opening velocities were 0.35-0.96 mm/h, approximately one-third to two-thirds pre-MDT velocities. A 0.5°C ambient temperature drop delayed MDT by 6.5 h amongst equi-sized specimens of the same strength. Generally, MDT correlated with material strength (irrespective of ambient temperature or specimen size), whereas time to first crack was more influenced by temperature. Also, SCDA reapplication proved effective for incompletely cracked specimens.

An Alternative to Conventional Rock Fragmentation Methods Using SCDA: A Review

Global energy and material consumption are expected to rise in exponential proportions during the next few decades, generating huge demands for deep earth energy (oil/gas) recovery and mineral processing. Under such circumstances, the continuation of existing methods in rock fragmentation in such applications is questionable due to the proven adverse environmental impacts associated with them. In this regard; the possibility of using more environmentally friendly options as Soundless Chemical Demolition Agents (SCDAs) play a vital role in replacing harmful conventional rock fragmentation techniques for gas; oil and mineral recovery. This study reviews up to date research on soundless cracking demolition agent (SCDA) application on rock fracturing including its limitations and strengths, possible applications in the petroleum industry and the possibility of using existing rock fragmentation models for SCDA-based rock fragmentation; also known as fracking. Though the expansive properties of SCDAs are currently used in some demolition works, the poor usage guidelines available reflect the insufficient research carried out on its material’s behavior. SCDA is a cementitious powdery substance with quicklime (CaO) as its primary ingredient that expands upon contact with water; which results in a huge expansive pressure if this CaO hydration reaction occurs in a confined condition. So, the mechanism can be used for rock fragmentation by injecting the SCDA into boreholes of a rock mass; where the resulting expansive pressure is sufficient to create an effective fracture network in the confined rock mass around the borehole. This expansive pressure development, however, dependent on many factors, where formation water content creates a negative influence on this due to required greater degree of hydration under greater water contents and temperature creates a positive influence by accelerating the reaction. Having a precise understanding of the fracture propagation mechanisms when using SCDA is important due to the formation of complex fracture networks in rocks. Several models can be found in the literature based on the tangential and radial stresses acting on a rock mass surrounding an SCDA charged borehole. Those fracture models with quasi-static fracturing mechanism that occurs in Mode I type tensile failure show compatibility with SCDA fracturing mechanisms. The effect of borehole diameter, spacing and the arrangement on expansive pressure generation and corresponding fracture network generation is important in the SCDA fracturing process and effective handling of them would pave the way to creating an optimum fracture network in a targeted rock formation. SCDA has many potential applications in unconventional gas and oil recovery and in-situ mining in mineral processing. However, effective utilization of SCDA in such application needs much extensive research on the performance of SCDA with respect to its potential applications, particularly when considering unique issues arising in using SCDA in different applications.

Cold and moderate ambient temperatures effects on expansive pressure development in soundless chemical demolition agents

This paper explores cool and moderate temperature (2–19°C) impacts on hydration heat and expansive pressure development in two commercial soundless chemical demolition agents (SCDAs). Experimental results showed (1) product-specific, linear relationships between the ambient temperature and time to peak hydration heat; (2) peak hydration heats to be consistently 1.5 times the ambient temperatures at 10–19°C; outside of this range the factor was greater; (3) a linear relationship between peak hydration heat time and the onset of expansive pressure development; (4) a largely proportional relationship between ambient temperature and volumetric expansion of 1.1–1.4 times the original volume.

CAS and ABM-based Demolition Waste Management Research in the AEC Industry

With the increase of the urban population and the rapid development of urbanization in China, a large number of old buildings will be demolished and produce a huge amount of waste. Currently the recycling ratio of old building materials is very low, which results in the problems of resource waste and environment pollution. This greatly challenges urban sustainable development. With respect to the continual growth of demolition waste quantities, it is urgent to research how to implement effective management of demolition wastes by focusing on the demolition agents' behavior. Based on the theory of complexity, this paper analyzes the demolition waste management from the perspective of complex adaptive system. Taking into account the green demolition (building dismantling) and conventional demolition (build- ing demolished) methods, the agent-based modeling method with Repast Simphony platform is applied to simulate interactions between demolition agents. The longitudinal trend of demolition waste quantities is forecasted.

ＡＥ震源分布からみた静的破砕剤による破砕における熱応力の影響について

Calcium oxide (CaO)-based expansive cement, also known as “non-explosive demolition agents”, has been widely used to fracture massive rocks and concrete structures. When water is added to expansive cement, calcium oxide reacts with water, and changes into calcium hydroxide expanding 1.96 times larger in volume with generating heat. In previous researches, although expansive pressure due to the volume increase has been only focused, effect of thermal stress induced by the heat has not been carefully discussed. In this meaning, the fracture mechanism of calcium oxide-based expansive cement has not been clarified.To clarify the fracture mechanism, the authors made an experiment to fracture a mortar specimen of 300 mm cubic by setting a calcium oxide-based expansive cement in a 48 mm diameter hole bored in the center of the specimen. AE (acoustic emission) sources clustered on a middle part of the shortest line between the borehole wall and one of the lateral surfaces, just before macroscopic cracks generated. This suggests that macroscopic cracks originated between the borehole wall and the lateral surface rather than the vicinity of the hole. From the elastic theory, although the expansive pressure causes tensile stress in tangential direction of the hole, the stress is the maximum at the hole-wall and decrease in proportion to square of the distance from the hole. On the other hand, thermal stress due to heating of the hole is tensile away from a certain distance from the hole. Thus, it could be concluded that thermal stress has large effects in the fracture caused by the calcium oxide-based expansive cement, at least, in a rock or concrete block without preexisting crack.

Enhancing Performance of Soundless Chemical Demolition Agents

Soundless chemical demolition agents (SCDAs) have been used in a variety of circumstances where other more conventional means of demolition were not feasible. When compared with conventional explosives, SCDAs are not yet economically competitive. Research was conducted on SCDAs to examine the possibility of adding an inert material (sand) to the SCDA in order to extend the material. Results show that although the expansive pressure generated by the SCDA is reduced by adding sand, reduction is not commensurate with the amount of sand added. Research was also conducted in order to determine if the workability of the SCDA slurry could be improved by adding a superplasticizer. These tests were conducted at water contents below levels where conventional mixtures were too stiff to effectively deposit them in a borehole. Results show that a superplasticizer can effectively improve SCDA workability and that the resultant expansive pressure is greater than that which is possible without the superplasticizer.

Properties of soundless chemical demolition agents: J. Hinze & J. Brown, Journal of Construction Engineering & Management - ASCE, 120(4), 1994, pp 816–827

Properties of soundless chemical demolition agents: J. Hinze & J. Brown, Journal of Construction Engineering & Management - ASCE, 120(4), 1994, pp 816–827

Properties of Soundless Chemical Demolition Agents

The traditional approach to demolish concrete structures or to reduce the sizes of large rocks or boulders has typically included the use of explosives. The resulting explosions are associated with the obvious risks posed by shock waves and fly rock. These, along with other detrimental side effects of using explosives, have increased an interest in the use of alternative methods to demolish rock and concrete structures. Soundless chemical demolition agents (SCDAs) have proven to be viable substitutes for the use of explosives. SCDAs are powdery materials that will expand considerably when mixed with water. This expansion, when occurring under confinement, generates significant expansive pressures. These pressures are sufficient to break up rock and concrete when the SCDA is confined in a borehole or a series of boreholes. Experiments have been conducted with SCDAs to learn more about those variables that tend to hamper or enhance SCDA performance. Results show that the amount of mixing water and the ambient temperature are the most important variables in influencing the generation of SCDA expansive pressures.