Papers by Keyword: Accelerated Curing

Abstract: In the modern construction practice high amounts of fly ash are not accepted by the construction industry due to a slower rate of strength gain at early age. A study has been undertaken to hasten the hydration process by proposed accelerated curing method of high volume fly ash concrete. Large amount of cement (up to 70% by weight) has been replaced by fly ash. The test results of the compressive strength of accelerated cured mixtures gives about (87-100)% strength ratios from itsa28 days compressive strength within one day only. That indicates, the compressive strength at 28 days can be achieved within 1 day only by using proposed accelerated curing. The results of drying shrinkage show that, the drying shrinkage of mixtures under conventional and accelerated curing conditions are comparable and these results add further benefit of this proposed accelerated curing. Key word: accelerated curing, high volume fly ash , curing cycle, drying shrinkage, flow ability.

Abstract: This paper presents the results of an experimental investigation carried out on accelerated curing of Quaternary Blended Cement (QBC) Concrete with and without recycled aggregate. Cement is partially replaced with fly ash, micro silica and nanosilica to produce QBC Concrete. The variables of study include the grade of concrete, powder content and percentage of recycled aggregate. Two grades of concrete M-40 and M-60 were used in this investigation. Based on the earlier studies, fly ash and micro silica are kept constant as 20% and 10% respectively while nanosilica is varied as 2% and 3%. Three percentages of recycled aggregate as partial replacement of natural aggregate (0%, 50% and 75%) were used. Two methods of curing were employed; boiling water method and hot air curing. The test results are encouraging and it is observed that 90% of the design strength could be achieved in one day for both the grades of concrete by curing at 100°C for a period of 3 hours. Keywords: Quaternary Blended Cement Concrete (QBCC), Fly ash (FA), Micro silica (SF), nanosilica (NSF), Recycled Concrete Aggregate (RCA), Accelerated Curing.

Abstract: In this paper, ｍade a PC beam specimen using ASR reactivity aggregate made in Chinese Zhejiang Ministry and made them do an accelerated curing and the influence by which swell of ASR reactivity aggregate gives it to a PC beam specimen was evaluate. Moreover the PC beam specimen which degraded by swell was classified every degradation grade, a loading test was put into effect and the load carrying capacity was inspected. As a result, I got the following conclusion. ①The thing which classifies the degradation grade into 3 stages (incubation period, acceleration period and degradation period) from the accelerated curing results of the test piece performed in advance. In the incubation period, it was confirmed that the compressive strength and the modulus of static elastic tend to increase more than before accelerated curing. ②Expansion of PC beam specimen was inflated from the upper edge part with less influence of prestress, Moreover as the expansion stabilized, the tendency of the lower edge portion which is highly affected by the prestress to expansion could be confirmed from the strain behavior by monitoring.In addition, with expansion of the lower edge part the prestress amount of the PC steel material placed inside the PC beam specimen (The lower edge position) is increasing and as the prestress amount stabilizes the tendency of expansion of the lower edge part is stabilized can also be confirmed. ③When accelerated curing was further promoted, the expansion of the upper edge and lower edge turned to a decreasing trend, and it was confirmed that stabilize tendency at about 25 to 35% of the maximum expansion. ④The P-δ curve up to fracture was measured for PC beam specimen before accelerated curing and ② to ③. As a result, it was not possible to confirm a large difference at the P-δ curve before accelerated curing and ②, but a significant decrease in load bearing capacity was confirmed at ④.

Abstract: Microwave energy is applied to cure cement-based materials with microwave power and time of application. First, the dielectric permittivity of them during a 24-hour first-hydration period at a frequency of 2.45 ± 0.05 GHz is measured and analyzed. Second, the characteristics of hardened cement paste as subjected to microwave energy with multi-mode rectangular wave guide, with specific attention to temperature rise, microstructure and development. This article presents a theoretical analysis to relate the compressive strengths of the CBM when subjected to microwave energy at an operating frequency of 2.45 GHz with a multi-mode cavity. The effects of water-to-solid mass ratios, aggregates, pozzolan materials, microwave power levels, application times, sequential processes, delay times, and comparisons with conventional curing (lime saturated-deionized water) were taken into account. The results indicated that for increasing the compressive strength, the main coefficient (a) as the Richards model are up to the highest value, the optimal energy level (microwave power × application time) should be in the range of 2.0 to 3.0 KJ when the specimen size was of  70.0 mm  40.0 mm in order to avoid the position of highest electric field strength within the cavity. Furthermore, the calculated compressive strengths based on the maturity concept overestimated the strength during 28 day first hydration time of the microwave-cured cement-based materials using the formula:

Abstract: Carbonation curing was adopted to accelerate the hydration of foam concrete with lower density of around 450 kg/m³. After standard curing in mold for 2d, the foam concrete samples were marked into two groups. The first one is directly cured in ‘Carbonation Test Chamber for Concrete’ with CO₂ concentration 20%, RH 70% and temperature 20°C (it was called ‘carbonation curing’) for 3d to 56d. The second one is cured in ‘Standard Curing Room for Concrete’ with RH ≥95% and temperature 20°C (it was called ‘standard curing’) for 7d, and then at carbonation curing for 3d, 7d and 21d. The strengths of harden foam concrete were tested, the hydration products were analyzed by means of XRD and TG/DSC. The results were compared with those of standard curing samples. It indicates that foam concrete with lower density is easier to be carbonated; the hydration of both C₃S and C₂S accelerates by carbonation curing, which results in higher early strength improvement. Vaterite is popular in the second group of samples, while it only appears in the first group of sample with longer carbonation time of 56d. Vaterite was considered to be formed from the further carbonation of C_xSH_y.