Effects of Total Internal Water Content on Freeze-Thaw Durability and Scaling Resistance of Internally-Cured Concrete

The effects of total internal (TI) water, provided by normalweight coarse and fine aggregates and pre-wetted fine lightweight aggregate (LWA), in the range of 6.8 to 17.3%, corresponding to internal curing (IC) water in the LWA ranging from 0 to 15.1%, by weight of cementitious materials, on the freeze-thaw durability and scaling resistance of 12 concrete mixtures are evaluated. Cementitious materials consist of portland cement only or portland cement with a 30% weight replacement by slag cement. The coarse aggregate consists of limestone (with an oven-dry absorption of 1.8%) or granite (with an oven-dry absorption of 0.6%), which provide 5.5 to 5.6% or 1.9% internal curing water by the weight of cementitious materials, respectively.All of the mixtures with the limestone coarse aggregate failed the test, with the average dynamic modulus of elasticity (EDYN) dropping below 95% of the initial value well before the 660 freeze-thaw cycles specified by the Kansas Department of Transportation, demonstrating that the limestone itself is susceptible to freeze-thaw damage. The mixtures containing granite coarse aggregate had an average relative EDYN above 95% of the initial value at 660 freeze-thaw cycles in the test of freeze-thaw durability at TI water contents up to 15.7% (corresponding to an IC water content of 13.4% from the LWA) by the weight of cementitious materials. The only mixture with granite coarse aggregate that failed the test had a 30% weight replacement of portland cement with slag cement and a TI water content of 17.3% by weight of the cementitious materials (corresponding to 15.1% IC water from LWA). This result indicates that it is possible to have too much internal curing water. In the scaling test, the mixtures with granite coarse aggregate, all of which contained LWA, had lower mass losses than mixtures with limestone coarse aggregate, although all but one of the 12 mixtures passed the test with a cumulative 56-day mass loss below 0.1 lb/ft2. For concrete with granite coarse aggregate, the mass loss increased slightly with increased TI water content when portland cement was used as the only cementitious material. When a 30% weight replacement of portland cement with slag cement was used, the mass loss increased for a TI water content above 12.5% (corresponding to 9.9% IC water from LWA), but remained below the failure limit, suggesting no benefits for a TI water content above 12.5% by the weight of cementitious materials. The mixtures with portland cement as the only cementitious material had lower mass losses than the mixtures with a 30% weight replacement of portland cement with slag cement for the same coarse aggregate. Pre-wetted fine lightweight aggregate (LWA) for internal curing (IC) should equal 7 to 8% by weight of cementitious materials. The results provide no evidence that it would be advantageous to stray much above these values and demonstrate that high TI/ IC water contents can be deleterious

Effects of Total Internal Water Content on Freeze-Thaw Durability and Scaling Resistance of Internally-Cured Concrete

The effects of total internal (TI) water, provided by normalweight coarse and fine aggregates and pre-wetted fine lightweight aggregate (LWA), in the range of 6.8 to 17.3%, corresponding to internal curing (IC) water in the LWA ranging from 0 to 15.1%, by weight of cementitious materials, on the freeze-thaw durability and scaling resistance of 12 concrete mixtures are evaluated. Cementitious materials consist of portland cement only or portland cement with a 30% weight replacement by slag cement. The coarse aggregate consists of limestone (with an oven-dry absorption of 1.8%) or granite (with an oven-dry absorption of 0.6%), which provide 5.5 to 5.6% or 1.9% internal curing water by the weight of cementitious materials, respectively. All of the mixtures with the limestone coarse aggregate failed the test, with the average dynamic modulus of elasticity (EDYN) dropping below 95% of the initial value well before the 660 freeze-thaw cycles specified by the Kansas Department of Transportation, demonstrating that the limestone itself is susceptible to freeze-thaw damage. The mixtures containing granite coarse aggregate had an average relative EDYN above 95% of the initial value at 660 freezethaw cycles in the test of freeze-thaw durability at TI water contents up to 15.7% (corresponding to an IC water content of 13.4% from the LWA) by the weight of cementitious materials. The only mixture with granite coarse aggregate that failed the test had a 30% weight replacement of portland cement with slag cement and a TI water content of 17.3% by weight of the cementitious materials (corresponding to 15.1% IC water from LWA). This result indicates that it is possible to have too much internal curing water. In the scaling test, the mixtures with granite coarse aggregate, all of which contained LWA, had lower mass losses than mixtures with limestone coarse aggregate, although all but one of the 12 mixtures passed the test with a cumulative 56-day mass loss below 0.1 lb/ft2. For concrete with granite coarse aggregate, the mass loss increased slightly with increased TI water content when portland iv cement was used as the only cementitious material. When a 30% weight replacement of portland cement with slag cement was used, the mass loss increased for a TI water content above 12.5% (corresponding to 9.9% IC water from LWA), but remained below the failure limit, suggesting no benefits for a TI water content above 12.5% by the weight of cementitious materials. The mixtures with portland cement as the only cementitious material had lower mass losses than the mixtures with a 30% weight replacement of portland cement with slag cement for the same coarse aggregate. Pre-wetted fine lightweight aggregate (LWA) for internal curing (IC) should equal 7 to 8% by weight of cementitious materials. The results provide no evidence that it would be advantageous to stray much above these values and demonstrate that high TI/ IC water contents can be deleterious

Evaluation of Cracking Performance of Bridge Decks Incorporating Nonmetallic Fibers

The Minnesota Department of Transportation (MnDOT) identified 20 monolithic (onecourse) bridge decks, constructed between 2015 and 2018, for cracking surveys to investigate the effectiveness of nonmetallic fibers in reducing bridge deck cracking. Of the 20 monolithic decks, 13 were constructed with concrete mixtures containing nonmetallic fibers and seven without fibers. Of the bridge decks constructed with nonmetallic fibers, nine are supported by precast-prestressed concrete girders and four are supported by steel girders. Of the decks constructed without fibers, six are supported by precast-prestressed concrete girders and one is supported by steel girders. The first portion of the report (Chapters 1 through 4) presents a description of the crack survey procedures, followed by information about the decks. A comparison of the decks is then made by converting the survey results to equivalent crack densities at 36 months of age. The second portion of the report (Chapters 5 and 6) investigates the effects of paste content, fibers, and construction procedures on the cracking performance of the 20 bridge decks surveyed in this study using comparisons with the results of crack surveys of 74 other bridge deck placements, conducted in Kansas, Virginia, and Indiana. Results show that for the decks surveyed in this study, the majority of cracks that contributed to crack density had lengths greater than 1 ft and there is no apparent correlation between the use of fibers and crack width. Low cracking bridge decks require the use of concrete with a low paste content (27.1% or less), and when the paste content is 27.1% or less, there is no significant difference in the average 36-month crack densities between bridge decks with and without fibers. More generally, good construction practices are needed for low-cracking decks, and with poor construction practices, even decks with low paste content, with or without fibers, can exhibit high crackin

Simple guidelines to minimise exposure to earthquake-triggered landslides

Reducing landslide risk in many mountainous regions is most effectively achieved by reducing exposure to landslides, because landslides cannot be predicted or stopped and engineering solutions are generally impractical or impossible. Because landslide hazard is very site-specific, available hazard maps may not be detailed enough, or contain appropriate and up-to- date information, to inform decision-making. We use our experience of studying the characteristics of landslides in recent large earthquakes to describe three simple guidelines that can be used to minimise exposure to future earthquake-triggered landslide hazard. The most effective measure is to choose a location that minimises the angle to the skyline, and to keep that angle below 25° if at all possible. It is also important to avoid steep channels (those with slopes of >15°), especially if there are many steep hillsides upstream. Finally, the slope of the ground at your location should always be minimised. These guidelines do not specify where landslides will occur, but can be used to distinguish between areas which are more or less likely to be affected by landslides in a large earthquake. They can be used to reduce risk before an earthquake occurs by helping to inform decisions on where to situate key infrastructure, such as schools or health posts. They can be used to inform decisions about the locations of houses, markets, or other areas where people are likely to spend considerable periods of time, or for deciding on appropriate types of land use. The guidelines can also be used in disaster preparedness and response planning, by identifying suitable evacuation routes and open spaces for use as evacuation sites or emergency shelters. We provide some brief guidance on what to do immediately after an earthquake in order to minimise exposure to landslides, and discuss the relevance of these guidelines for protecting against rainfall-triggered landslides which may occur more frequently

Earthquake Risk Reduction Efforts in Nepal: NSET’s Experience

This chapter describes earthquake risk reduction efforts in Nepal from NSET’s perspective and is co-authored by a team of researchers who have been with NSET since its inception. NSET was established in 1994 with the objective to reduce earthquake risk in Nepal. The usefulness and innovativeness of NSET’s long-term efforts were tested by the Gorkha earthquake, highlighting positive impacts of the risk management efforts in Nepal in the past 22 years. This chapter provides a brief history of NSET’s earthquake risk management efforts in Nepal and sheds light on some of the innovative postulations and methodologies used