Developing a Simple and Rapid Test for Monitoring the Heat Evolution of Concrete Mixtures for Both Laboratory and Field Applications, January 2006

Various test methods exist for measuring heat of cement hydration; however, most current methods require expensive equipment, complex testing procedures, and/or extensive time, thus not being suitable for field application. The objectives of this research are to identify, develop, and evaluate a standard test procedure for characterization and quality control of pavement concrete mixtures using a calorimetry technique. This research project has three phases. Phase I was designed to identify the user needs, including performance requirements and precision and bias limits, and to synthesize existing test methods for monitoring the heat of hydration, including device types, configurations, test procedures, measurements, advantages, disadvantages, applications, and accuracy. Phase II was designed to conduct experimental work to evaluate the calorimetry equipment recommended from the Phase I study and to develop a standard test procedure for using the equipment and interpreting the test results. Phase II also includes the development of models and computer programs for prediction of concrete pavement performance based on the characteristics of heat evolution curves. Phase III was designed to study for further development of a much simpler, inexpensive calorimeter for field concrete. In this report, the results from the Phase I study are presented, the plan for the Phase II study is described, and the recommendations for Phase III study are outlined. Phase I has been completed through three major activities: (1) collecting input and advice from the members of the project Technical Working Group (TWG), (2) conducting a literature survey, and (3) performing trials at the CP Tech Center’s research lab. The research results indicate that in addition to predicting maturity/strength, concrete heat evolution test results can also be used for (1) forecasting concrete setting time, (2) specifying curing period, (3) estimating risk of thermal cracking, (4) assessing pavement sawing/finishing time, (5) characterizing cement features, (6) identifying incompatibility of cementitious materials, (7) verifying concrete mix proportions, and (8) selecting materials and/or mix designs for given environmental conditions. Besides concrete materials and mix proportions, the configuration of the calorimeter device, sample size, mixing procedure, and testing environment (temperature) also have significant influences on features of concrete heat evolution process. The research team has found that although various calorimeter tests have been conducted for assorted purposes and the potential uses of calorimeter tests are clear, there is no consensus on how to utilize the heat evolution curves to characterize concrete materials and how to effectively relate the characteristics of heat evolution curves to concrete pavement performance. The goal of the Phase II study is to close these gaps.

Field Evaluation of Cold In-Place Recycling of Asphalt Concrete, HR-303, 1993

The average thickness of the existing asphalt cement concrete (ACC) along route E66 in Tama County was 156 mm (6.13 in.). The rehabilitation strategy called for widening the base using the top 75 mm (3 in.) of the existing ACC by a recycling process involving cold milling and mixing with additional emulsion/rejuvenator. The material was then placed into a widening trench and compacted to match the level of the milled surface. The project had the following results: (1) Cold recycled ACC pavement provided adequate pavement structure for a low volume road; (2) Premature cracking of the ACC in the widened pavement area was caused by compaction of the mix over a saturated subgrade; and (3) Considerably less transverse and longitudinal cracking was observed with 75 mm (3 in.) of cold recycled ACC and a 50 mm (2 in.) hot mix ACC overlay than with a conventional hot mix overlay with no cold recycling. More research should be done on efficient construction procedures and incorporating longer test sections for proper evaluation.

Heat Dissipation and Crack Control in Massive Concrete at the Burlington Bridge, MLR-94-1, 1995

The large concrete placements at the Burlington Bridge were expected to cause great temperature differentials within the individual placements. In an attempt to reduce cracking due to the large temperature differentials, the Iowa Department of Transportation required that contractors continuously monitor the temperatures and temperature differentials in the concrete placement to assure that the temperature differentials did not exceed 35 deg F. It was felt that if temperature differentials remained below 35 deg F, cracking would be minimized. The following is a summary of the background of the project, and what occurred during individual concrete placements. The following conclusions were drawn: 1) Side temperatures are cooler and more greatly affected by ambient air temperatures; 2) When the 35 deg F limit was exceeded, it was almost exclusively the center to side differential; 3) The top temperature increases substantially when a new pour is placed; 4) The use of ice and different cement types did seem to affect the overall temperature gain and the amount of time taken for any one placement to reach a peak, but did not necessarily prevent the differentials from exceeding the 35 deg F limit, nor prevent cracking in any placement; and 5) Larger placements have a greater tendency to exceed the differential limit.

Recycling of Portland Cement Concrete Roads in Iowa, MLR-77-6, 1977

We are depleting the once seemingly endless supply of aggregate available for concrete paving in Iowa. At the present time, some parts of our state do not have locally available aggregates of acceptable quality for portland cement concrete paving. This necessitates lengthy truck and rail hauls which frequently more than doubles the price of aggregate. In some parts of the state, the only coarse aggregates available locally are "d-cracking" in nature. Iowa's recycling projects were devised to alleviate the shortage of aggregates wherever they were found to have an economic advantage. We completed our first recycling project in 1976 on a 1.4 project in Lyon county. The data collected in this project was used to schedule two additional projects in 1977. The larger of these two projects is located in Page and Taylor county on Highway #2 and is approximately 15 miles in length. This material is to be crushed and re-used in the concrete paving, it is to be reconstructed on approximately the same alignment. The second project is part of the construction of Interstate I-680 north of council Bluffs where an existing 24 foot portland cement concrete roadway is to be recycled and used as the aggregate in the slip form econocrete subbase and the portland cement concrete shoulders.

Recycling of Cass County I-80 Asphalt Concrete, Progress Report, HR-1011, 1977

Approximately 40,000 tons of slightly damaged asphalt concrete has been removed from Interstate 80 in Cass and stockpiled. Laboratory tests had indicated that this material had considerable value when upgraded with new aggregate and asphalt cement. This report documents the procedures used and results obtained on an experimental recycling project. It was demonstrated that present drum mixing-recycling equipment and procedures can be used to utilize this material with satisfactory results. Laboratory analyses of material components and mixtures were performed; these analyses indicate mixture can be produced that is uniform, stable, and very closely resembles mixture produced with all new material. Follow~up evaluations will be made to determine the effects of traffic and environment. Preliminary data indicate that plans should be made to incorporate the stockpiled material in projects near the stockpile site.

Recycling of Asphalt Concrete From I-80 in Cass County, HR-1011, 1978

Approximately 40,000 tons of deteriorated asphalt concrete has been removed from Interstate 80 in Cass County and stockpiled. Laboratory tests indicate that this material has considerable value when upgraded with new aggregate and asphalt cement. This report documents the procedures used and results obtained on an experimental recycling project. It was demonstrated that present drum mixing-recycling equipment and procedures can be used to utilize this material with satisfactory results. Laboratory analyses of material components and mixtures were performed; these analyses indicate mixture can be produced that is uniform, stable, and very closely resembles mixture produced with all virgin material. A 1700 foot long test section was constructed on US 169 in Kossuth County wherein salvaged asphalt concrete from I-80 in Cass County was utilized. The salvaged mix was blended with virgin aggregate and recycled through a modified drum mixing plant, the reprocessed mixture was satisfactorily placed 1 1/2 inches thick as a resurfacing course on an old PCC pavement. An inspection of the test section was made in December of 1978 to evaluate the performance after one full year of service. There was no evidence of rutting or shoving from traffic. The surface does, however, have a very dry and somewhat ravelled appearance. This can be related to a low asphalt content in the mix and some temperature control problems which were difficult to get fully corrected on such a short project and with a short supply of readily available materials.

Field Evaluation of Cold In-Place Recycling of Asphalt Concrete, HR-303, Construction Report, 1990

There are still many vintage portland cement concrete (PCC) pavements, 18 ft wide (5.4 m), dating back to pre-World War II era in use today. Successive overlays have been placed to cover joints and to improve rideability. The average thickness of the existing asphalt cement concrete (ACC) along route E66 in Tama County, Iowa, was 6.13 in. (15.6 cm). The rehabilitation strategy called for widening the base using the top 3 in. (7.6 cm) of the existing ACC by a recycling process involving cold milling and mixing with additional emulsion/rejuvenator. The material was then placed into a widening trench and compacted to match the level of the milled surface. This project was undertaken to develop a rehabilitation methodology to widen these older pavements economically and to have a finished surface capable of carrying traffic with little or no additional work.

Physiological evaluation of heat stress in gestating sows under different housing systems in bedding and concrete floor

The purpose of this paper was to observe the use of bedding (wood shavings) in physiological variables that indicate thermal stress in gestating sows. The experiment was conducted in order to evaluate the effect of two types of floor (concrete and wood shavings). Worse microclimatic conditions were observed in bedding systems (P<0.05), with an increase in temperature and enthalpy of 1.14 ºC and 2.37 kJ.kg dry air-1, respectively. The floor temperature at the dirty area was higher in the bedding presence in comparison to its absence. In spite of the worse microclimatic conditions in the bedding, the rectal temperature did not differ significantly (P>0.05) but the skin surface temperature was higher in the bedding systems. The same occurred with the respiratory rates. The physical characteristics of the floor material influenced the rate of heat loss by conductance. Estimated values were 35.04 and 7.99 W m-2 for the conductive heat loss between the animal and floor for treatments with or without bedding, respectively. The use of bedding in sow rearing has a negative impact on microclimatic conditions, what implies in thermoregulatory damages.

Recycling scrap automotive heat shield insulation material

Automotive heat shields are usually composed of two metal sheets enclosing an insulating material with a paper-like texture that contains refractory ceramic particles. This article discusses the results achieved by recycling the scrap automotive insulation that is discarded in landfills, using the same concept as paper recycling. For comparison with the original product, tests of thickness, bulk density, weight loss on ignition, tensile strength, compressibility, and recovery were performed on recycled materials produced in a so-called "manual" process (involving little automation and performed in adapted facilities) without pressing, and pressed once, twice, and four times. Materials recycled in a so-called "industrial" process (in a paper recycling plant) without pressing, and pressed once were also tested. The recycled materials can be considered approved with respect to the main requirement, thermal insulation, since they dissipated the under-hood temperature by more than 300 A degrees C (like the original product). Like the heat insulation tests, the thermogravimetric analysis suggested that the recycled materials showed higher stability than the original product. Thermogravimetric, microscopy, and energy dispersive spectroscopy analyses indicated that the structural and compositional characteristics of the original product were preserved after recycling.

Study of the Influence of Fines on a Self-Compacting Concrete

The paper presents the results of the tests of a self-compacting concrete made with fines which include Portland cement and three fillers: hornfels, limestone and metakaolin, in a weight proportion between 23% and 45% of the admixtures. The first mix proportions were designed with a high proportion of Portland cement (720-750kg/m3), and are compared to those having a smaller content of cement and more fillers. The results obtained show that the limestone filler percentage should be higher than the hornfels one, and both of them significantly higher than that of the metakaolin so as to facilitate the fluidity and self-compactability. AIso, the higher proportion of fillers causes a rounded porosity in the mixing which has a bearing on better compressive strength results.

Recycling of asphalt concrete airfield pavement : a laboratory study /

Performing organization : Civil Enginnering Laboratory. Naval Construction Battalion Center

Coupled heat and mass transfer in concrete exposed to fire

The first investigation of this study is concerned with the reasonableness of the assumptions related to diffusion of water vapour in concrete and with the development of a diffusivity equation for heated concrete. It has been demonstrated that diffusion of water vapour does occur in concrete at all temperatures and that the type of diffusion is concrete is Knudsen diffusion. Neglecting diffusion leads to underestimating the pressure. It results in a maximum pore pressure of less than 1 MPa. It has also been shown that the assumption that diffusion in concrete is molecular is unreasonable even when the tortuosity is considered. Molecular diffusivity leads to overestimating the pressure. It results in a maximum pore pressure of 2.7 MPa of which the vapour pressure is 1.5 MPa while the air pressure is 1.2 MPa. Also, the first diffusivity equation, appropriately named 'concrete diffusivity', has been developed specifically for concrete that determines the effective diffusivity of any gas in concrete at any temperature. In thick walls and columns exposed to fire, concrete diffusivity leads to a maximum pore pressures of 1.5 and 2.2 MPa (along diagonals), respectively, that are almost entirely due to water vapour pressure. Also, spalling is exacerbated, and thus higher pressures may occur, in thin heated sections, since there is less of a cool reservoir towards which vapour can migrate. Furthermore, the reduction of the cool reservoir is affected not only by the thickness, but also by the time of exposure to fire and by the type of exposure, i.e. whether the concrete member is exposed to fire from one or more sides. The second investigation is concerned with examining the effects of thickness and exposure time and type. It has been demonstrated that the build up of pore pressure is low in thick members, since there is a substantial cool zone towards which water vapour can migrate. Thus, if surface and/or explosive spalling occur on a thick member, then such spalling must be due to high thermal stresses, but corner spalling is likely to be pore pressure spalling. However, depending on the exposure time and type, the pore pressures can be more than twice those occurring in thick members and thought to be the maximum that can occur so far, and thus the enhanced propensity of pore pressure spalling occurring on thin sections heated on opposite sides has been conclusively demonstrated to be due to the lack of a cool zone towards which moisture can migrate. Expressions were developed for the determination of the maximum pore pressures that can occur in different concrete walls and columns exposed to fire and of the corresponding times of exposure.

Chemical composition of mixed construction and demolition recycled aggregates from the State of Sao Paulo

Construction and Demolition Waste (CDW) represents. about 50% of the total Brazilian municipal solid waste: thus, recycling represents huge benefits both in environmental and economic perspectives. Herein, the chemical characterization results of three samples from two different recycling plants from the State of Sao Paulo is prevented. The results demonstrated that the visual classification into grey and red is not related to the chemical composition but mostly to the grain size fraction. The chemical composition of the CDW varies according to the content of cement paste, natural aggregates (quartz sand or granite), red ceramic and clay. Furthermore, the production of recycled concrete aggregates requires two crushing stages to meet the technical standards. The sand fraction (below 4.8 mm) presents high grades of SiO(2), which indicates the liberation of cement paste to fines (< 0.15 mm). The fines have a great potential to be used in the cement industry.

Physical-chemical and mineralogical characterization of fine aggregates from construction and demolition waste recycling plants

Construction and demolition waste (CDW) represents around 31% of all waste produced in the European Union. It is today acknowledged that the consumption of raw materials in the construction industry is a non-sustainable activity. It is thus necessary to reduce this consumption, and the volume of CDW dumped, by using this waste as a source of raw materials for the production of recycled aggregates. One potential use of these aggregates is their incorporation in reinforced concrete as a replacement of natural aggregates. A concrete that incorporates these aggregates and still performs well requires them to be fully characterized so that their behaviour within the concrete can be predicted. Coarse recycled aggregates have been studied quite thoroughly, because they are simpler to reintroduce in the market as a by-product, and so has the performance of concrete made with them. This paper describes the main results of research designed to characterize the physical and chemical properties of fine recycled aggregates for concrete production and their relationship with mineralogical composition and preprocessing. The constraints of the incorporation of fine aggregates in reinforced concrete are discussed. It is shown that, unless a developed processing diagram is used, this application is not feasible. (C) 2013 Elsevier Ltd. All rights reserved.