Performance of Precast Bridge Girder Materials

Performance of Precast Bridge Girder Materials

Technical review

 

The  article published by Tiburzi, Drimala and Folliard in 2017, under the title “Evaluation of precast bridge girder cracking: The role of volume change”, focuses on mitigating from the theory of connecting cracking in precast bridges with ASR and/or DEF phenomena while examining the impact of internal volume change, pooling together results from subsets of concrete mixtures [1]. Timely and important, this topic links results by other researches on the controlled and experimental environment, with original research, stating that “Research is in progress to evaluate the possibility of low w/cm mixtures that have a high amount of unhydrated cement hydrating upon exposure to external moisture.” [1]. The article uses various case studies based approach to validate and to allow deeper understanding of time-dependent factors, that lead to improvement of cracking resistance, emphasizing effects of water-cementitious material ratio as more pronounced to fresh and hardened properties in concrete including durability, drying shrinkage and potential for cracking, when compared to other alternatives [1].

Given an outline of the testing approach and high scientific merit sources, this study includes also recreation of previously conducted experiments by Ideker, Tazawa, and Miyazawa [1]. Each test is described in details regarding time-span, specimen cross-sectional dimensions and chemical mixture used [1]. This research study added developed graphs for autogenous deformation and/or stresses to comprehensively investigate the issue, but lacking a comparison between the graphs to consolidate a judgment on best design method to follow. The time-dependent analysis is carried out by establishing a stress-strain-time relationship for the concrete material. The stress/deformation of hardened concrete tests was based off of ASTM C 157 code method, which “covers the determination of the length changes that are produced by causes other than externally applied forces and temperature changes in hardened hydraulic-cement mortar and concrete specimens made in the laboratory and exposed to controlled conditions of temperature and moisture.” [1, 2]. There are very specific measurement amounts mentioned to provide an accurate description of the methodology. Additionally, the sources referenced in the journal article contribute to a seemingly high scientific merit.

In Table 1, the proportions of concrete mixture used throughout this study are displayed.

Table 1: Mixture proportions of concrete mixes (kg/m3).

Table 1 shows the concrete mixture proportions used in this study. Attaching the explanation given of how it is used in the beginning of the article, makes the table a useful tool for recreating the experiment and be prepared on what to expect as the study develops further. Moreover, authors emphasize in bolded letters the controlling concrete mixtures stating “For conciseness and convenience, each mixture shown in Table 1 will be designated by the use of a mixture code” highlighting the importance of this table [1]. No additional reference to this table was evident in the entire article [1]. Table 1 functions as informative and it can be easily converted into a short description including the results obtained after the experiment.


Figure 1 shows the effects of w/cm ratio presented by autogenous deformation curves.

.   Fig. 1. Autogenous deformation curves showing the effect of w/cm ratio.

Figure 1, as shown above, displays the results of autogenous deformation versus time (up to 7 days) of the various specimen under restricted thermal conditions. Information obtained by this figure is easy to follow and comprehend and matched accordingly with the goal of the study. Authors were able to describe the importance of the figure clearly, respecting all sorts of tests available so far. “The autogenous deformations measured during the 7- day tests for mixtures containing PC-III-A with w/cm between 0.28 and 0.42” [1] is a description that indicates conclusions are expected to be finalized based on the results of given data considering the trend of each line.

Generally, results of this study research on the properties and performance of precast bridge girder materials, novel experimental techniques, the latest analytical and modelling methods and the potential for improved materials. Overall, the article draws the conclusion that more research should be taken in order to perceive a better understanding of relevant volume changes at later ages [1]. It advances with state-of-the-art research, which concludes that “Mixtures containing w/cm at or below 0.31 showed an unusually high proportion of unhydrated cement present,” [1]. This information was determined by examining in microstructural level of cores extracted from different blocks subjected to various exposure conditions. After reviewing the article, my recommendations are as follows. When the material and methods were introduced, it is mentioned that there will be four polycarboxylate-based high-range water reducers, while in the results only two of them were distinguished. Despite the recommendation mentioned for Figure 1 and Table 1, there are some figures that give information on testing methods and exposure block pictures didn’t seem to add helpful information in reaching the results other than informative function of the experiment.  Instead, graphs on the most pronounced results for drying shrinkage can be added and numerically compared to the early-age volume changes. The entire article seems well written and organized in an easy to follow manner. Even though the conclusions did not include any tables/figures but referenced the ones of the results, the conclusions of the article were drawn in a logical manner justifying the original research. I also applaud the efficiency attained reaching the importance of the research revealed.

[1]  D. Thano, K.J. Folliard, N.B. Tiburzi, Evaluation of precast bridge girder cracking: The role of volume change, Cem. Con. Ref. 101 (2017) 55–67.

[2]  ASTM Standards. “Standard Test Method for Length Change of Hardened Hydraulic-Cement Mortar and Concrete” Retrieved from: https://www.astm.org


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