No abstract

In this study, the effects of soybean-urease-induced carbonate precipitation on a high-temperature damage repair of concrete were explored. C50 concrete specimens were exposed to high temperatures from 300 to 600 °C, then cooled to an ambient temperature and repaired by two different methods. The influences of the damage temperature and repair methods on surface film thickness, average infrared temperature increase, water absorption, and compressive strength were investigated. Scanning electron microscopy (SEM) images were carried out to further study the mechanism involved. The results revealed that the white sediments on the surface of the repaired specimens were calcium carbonate (CaCO3) and calcium oxalate (CaC2O4). The surface film thickness reached up to 1.94 mm after repair. The average infrared temperature increase in the repaired specimens at different damage temperatures was averagely reduced by about 80% compared with that before the repair. It showed more obvious repair effects at higher temperatures in water absorption and compressive strength tests; the compressive strength of repaired specimens was 194% higher than that before repairs at 600 °C. A negative pressure method was found to be more effective than an immersion method. This study revealed the utilization of SICP on repairing high-temperature damage of concrete is feasible theoretically.

Preliminary noteHow can people predict the sedimentation of tall buildings and analyze the foundation rebound to protect underground utilities? This is the urgent problem in today's construction. To solve it, this paper is dedicated to analyzing how piles affect the foundation rebound value by using Mohr-Coulomb Model and the 3D emulation calculation software FLAC3D with 20-meter-deep foundation pits as an example. The study shows that the distribution pattern of the foundation rebound without piles is a convex curve while piles make the curve go corrugated with the foundation rebound value shrieking by 0,4÷0,6. Also, parameters such as the distance of the piles and diameter of the piles and length of the piles have an effect on the value in a way that the increasing distance lowers the piles' restriction on the foundation rebound value. Therefore, this paper suggests that the largest distance between piles should be no more than 6d when the restricted extent of the value is about 0,23÷0,37. Raising the diameter and length of the piles (no more than 1,25 times of the digging depth) can restrict rebound effectively. Therefore, this paper concludes useful parameters in pile design, proves its mechanism for restriction on foundation rebound, and provides analytical basis for optimization of the piles. Keywords: Mohr-Coulomb Model principle; numerical imitation; piles; rebound Numerička analiza ograničenja pilota kod temeljenjaPrethodno priopćenje Kako je moguće predvidjeti taloženje visokih zgrada i analizirati pomak temelja kako bi se zaštitile podzemne komunalije? To je urgentan problem u današnjoj izgradnji. U svrhu njegovog rješenja, u ovom se radu istražuje kako piloti utječu na vrijednost pomaka temelja primjenom Mohr-Coulomb Modela i 3D računarskog programa FLAC3D s 20 m dubokim iskopima temelja kao primjerom. Analiza pokazuje da je distribucijski uzorak pomaka temelja bez pilota konveksna krivulja, a da s pilotima krivulja postaje valovita uz porast vrijednosti pomaka temelja za 0,4÷0,6. Isto tako parametri poput udaljenosti pilota, promjera pilota i njihove dužine utječu na tu vrijednost na način da veći razmak snižava ograničenje pilota na vrijednost pomaka temelja. Stoga se u radu predlaže da najveći razmak između pilota ne bi trebao biti veći od 6d kad je ograničeni iznos vrijednosti oko 0,23÷0,37. Povećanje promjera i dužine pilota (ne više od 1,25 puta dubine kopanja) može učinkovito ograničiti pomak. Prema tome, u radu se daju korisni parametri za konstrukciju pilota, dokazuje njihovo djelovanje na mehanizam za ograničenje pomaka temelja i pruža analitička osnova za optimizaciju pilota.

After exposure to high temperatures, the mechanical properties and durability of concrete structures are significantly reduced, and effective measures must be taken for reinforcement and repair. High-temperature concrete damage manifests as looseness, spalling, and cracks, which are suitable for microbial-induced carbonate precipitation. When repairing high-temperature concrete damage with microbial-induced carbonate precipitation (MICP), the calcium source is an important influencing factor. The type of calcium source and the method used to add calcium source will directly affect the mineralized products, which in turn affect the quality of the repair. In this study, the mineralized products of Sporosarcina pasteurii were qualitatively analyzed and the appropriate type of calcium source and addition method were determined. The repair effect on high-temperature concrete damage was also verified. The results showed that the mineralized products of Sporosarcina pasteurii were calcium carbonate, with mixed vaterite and calcite crystals. Calcium acetate was found to be the most appropriate calcium source, while the pre-calcium-source addition method was shown to be optimal. At each damage temperature, the compressive strength showed a certain degree of recovery, and the water absorption exhibited a certain degree of reduction. At 600 °C, the compressive strength of the repaired specimens increased up to 202.68% compared with the damaged specimens and the water absorption of the repaired specimens was 34.32% lower than that of the damaged specimens. The higher the damage temperature, the more obvious the repair effect.