Eco-efficient self-compacting concrete with reduced Portland cement content and high volume of fly ash and metakaolin

The eco-efficient, self-compacting concrete (SCC) production, containing low levels of cement in its formulation, shall contribute for the constructions' sustainability due to the decrease in Portland cement use, to the use of industrial residue, for beyond the minimization of the energy needed for its placement and compaction. In this context, the present paper intends to assess the viability of SCC production with low cement levels by determining the fresh and hardened properties of concrete containing high levels of fly ash (FA) and also metakaolin (MK). Hence, 6 different concrete formulations were produced and tested: two reference concretes made with 300 and 500 kg/m3 of cement; the others were produced in order to evaluate the effects of high replacement levels of cement. Cement replacement by FA of 60% and by 50% of FA plus 20% of MK were tested and the addition of hydrated lime in these two types of concrete were also studied. To evaluate the self-compacting ability slump flow test, T500, J-ring, V-funnel and L-box were performed. In the hardened state the compressive strength at 3, 7, 14, 21, 28 and 90 days of age was determined. The results showed that it is possible to produce low cement content SCC by replacing high levels of cement by mineral additions, meeting the rheological requirements for self-compacting, with moderate resistances from 25 to 30 MPa after 28 days.

Efeito do tempo e temperatura de cura em concretos autoadensáveis com reduzido teor de cimento

Os concretos com reduzidos teores de cimento têm sido foco de crescentes estudos em virtude do seu potencial quanto a sustentabilidade das construções. Mais recentemente o estudo ascendeu aos concretos autoadensáveis com reduzidos teores de cimento. Entretanto, há uma preocupação quanto ao ganho de resistência nas primeiras idades desses concretos devido ao baixo teor de cimento e o elevado teor de adições minerais que conhecidamente proporcionam melhorias nas resistências a longas idades, notadamente acima de 90 dias. O presente trabalho tem o objetivo de avaliar o ganho de resistência e a hidratação de concretos autoadensáveis com reduzidos teores de cimento e elevados teores de cinza volante e metacaulim, com e sem adição de hidróxido de cálcio. Para tanto, os concretos foram submetidos a cura por imersão em água a temperatura de 20±2ºC durante 3, 7, 14, 21, 28, 91 e 360 dias e também cura em água aquecida a 40ºC por 3 dias acrescidos de mais 3 dias a 60ºC e um dia de resfriamento dentro do banho térmico até a temperatura ambiente. Foram realizados ensaios de slump flow, L-box, V-test e J-ring para caracterização do CAA no estado fresco. No estado endurecido foram realizados ensaios de resistência à compressão a idades de 3, 7, 14, 28, 90 e 360 dias, absorção por capilaridade, difração de raios X e MEV. Os resultados demonstram a aptidão em desenvolver CAA com reduzidos teores de cimento devido a excelente capacidade das cinzas volantes e metacaulim em trabalharem como agentes viscosificadores dos concretos autoadensáveis. Verifica-se que é possível produzir CAA com consumos de cimento entre 150 e 200 kg/m3 que atinjam resistências aos 28 dias entre 25 e 40 MPa e entre 45 e 70 MPa, para cura úmida e térmica respectivamente. A partir do ensaios de MEV e DRX é possível inferir que o ganho de resistência obtido pelos CAA com cura térmica é devido a aceleração das reações pozolânicas e da estrutura interna mais densa dos concretos submetidos a cura térmica.

Análise da viabilidade económica das empresas de pavimentação rodoviária em cenário de crise

Dissertação de mestrado integrado em Engenharia Civil

FY2008 Annual Summary July 1, 2007 - June 30, 2008

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Task 4: Testing Iowa Portland Cement Concrete Mixtures for the AASHTO Mechanistic-Empirical Pavement Design Procedure, May 2008

The present research project was designed to identify the typical Iowa material input values that are required by the Mechanistic-Empirical Pavement Design Guide (MEPDG) for the Level 3 concrete pavement design. It was also designed to investigate the existing equations that might be used to predict Iowa pavement concrete for the Level 2 pavement design. In this project, over 20,000 data were collected from the Iowa Department of Transportation (DOT) and other sources. These data, most of which were concrete compressive strength, slump, air content, and unit weight data, were synthesized and their statistical parameters (such as the mean values and standard variations) were analyzed. Based on the analyses, the typical input values of Iowa pavement concrete, such as 28-day compressive strength (f’c), splitting tensile strength (fsp), elastic modulus (Ec), and modulus of rupture (MOR), were evaluated. The study indicates that the 28-day MOR of Iowa concrete is 646 + 51 psi, very close to the MEPDG default value (650 psi). The 28-day Ec of Iowa concrete (based only on two available data of the Iowa Curling and Warping project) is 4.82 + 0.28x106 psi, which is quite different from the MEPDG default value (3.93 x106 psi); therefore, the researchers recommend re-evaluating after more Iowa test data become available. The drying shrinkage (εc) of a typical Iowa concrete (C-3WR-C20 mix) was tested at Concrete Technology Laboratory (CTL). The test results show that the ultimate shrinkage of the concrete is about 454 microstrain and the time for the concrete to reach 50% of ultimate shrinkage is at 32 days; both of these values are very close to the MEPDG default values. The comparison of the Iowa test data and the MEPDG default values, as well as the recommendations on the input values to be used in MEPDG for Iowa PCC pavement design, are summarized in Table 20 of this report. The available equations for predicting the above-mentioned concrete properties were also assembled. The validity of these equations for Iowa concrete materials was examined. Multiple-parameters nonlinear regression analyses, along with the artificial neural network (ANN) method, were employed to investigate the relationships among Iowa concrete material properties and to modify the existing equations so as to be suitable for Iowa concrete materials. However, due to lack of necessary data sets, the relationships between Iowa concrete properties were established based on the limited data from CP Tech Center’s projects and ISU classes only. The researchers suggest that the resulting relationships be used by Iowa pavement design engineers as references only. The present study furthermore indicates that appropriately documenting concrete properties, including flexural strength, elastic modulus, and information on concrete mix design, is essential for updating the typical Iowa material input values and providing rational prediction equations for concrete pavement design in the future.

Optimizing Cementious Content in Concrete Mixtures for Required Performance Final Report, January 2012

This research investigated the effects of changing the cementitious content required at a given water-to-cement ratio (w/c) on workability, strength, and durability of a concrete mixture. An experimental program was conducted in which 64 concrete mixtures with w/c ranging between 0.35 and 0.50, cementitious content ranging from 400 to 700 per cubic yard (pcy), and containing four different supplementary cementitious material (SCM) combinations were tested. The fine-aggregate to total-aggregate ratio was fixed at 0.42 and the void content of combined aggregates was held constant for all the mixtures. Fresh (i.e., slump, unit weight, air content, and setting time) and hardened properties (i.e., compressive strength, chloride penetrability, and air permeability) were determined. The hypothesis behind this study is that when other parameters are kept constant, concrete properties such as strength, chloride penetration, and air permeability will not be improved significantly by increasing the cement after a minimum cement content is used. The study found that about 1.5 times more paste is required than voids between the aggregates to obtain a minimum workability. Below this value, water-reducing admixtures are of no benefit. Increasing paste thereafter increased workability. In addition, for a given w/c, increasing cementitious content does not significantly improve compressive strength once the critical minimum has been provided. The critical value is about twice the voids content of the aggregate system. Finally, for a given w/c, increasing paste content increases chloride penetrability and air permeability.

Optimizing Cementitious Content in Concrete Mixtures for Required Performance Final Report, January 2012

This research investigated the effects of changing the cementitious content required at a given water-to-cement ratio (w/c) on workability, strength, and durability of a concrete mixture. An experimental program was conducted in which 64 concrete mixtures with w/c ranging between 0.35 and 0.50, cementitious content ranging from 400 to 700 per cubic yard (pcy), and containing four different supplementary cementitious material (SCM) combinations were tested. The fine-aggregate to total-aggregate ratio was fixed at 0.42 and the void content of combined aggregates was held constant for all the mixtures. Fresh (i.e., slump, unit weight, air content, and setting time) and hardened properties (i.e., compressive strength, chloride penetrability, and air permeability) were determined. The hypothesis behind this study is that when other parameters are kept constant, concrete properties such as strength, chloride penetration, and air permeability will not be improved significantly by increasing the cement after a minimum cement content is used. The study found that about 1.5 times more paste is required than voids between the aggregates to obtain a minimum workability. Below this value, water-reducing admixtures are of no benefit. Increasing paste thereafter increased workability. In addition, for a given w/c, increasing cementitious content does not significantly improve compressive strength once the critical minimum has been provided. The critical value is about twice the voids content of the aggregate system. Finally, for a given w/c, increasing paste content increases chloride penetrability and air permeability.

Concrete Pavement Mixture Design and Analysis (MDA): Effect of Aggregate Systems on Concrete Properties, TPF-5(205), 2012

For years, specifications have focused on the water to cement ratio (w/cm) and strength of concrete, despite the majority of the volume of a concrete mixture consisting of aggregate. An aggregate distribution of roughly 60% coarse aggregate and 40% fine aggregate, regardless of gradation and availability of aggregates, has been used as the norm for a concrete pavement mixture. Efforts to reduce the costs and improve sustainability of concrete mixtures have pushed owners to pay closer attention to mixtures with a well-graded aggregate particle distribution. In general, workability has many different variables that are independent of gradation, such as paste volume and viscosity, aggregate’s shape, and texture. A better understanding of how the properties of aggregates affect the workability of concrete is needed. The effects of aggregate characteristics on concrete properties, such as ability to be vibrated, strength, and resistivity, were investigated using mixtures in which the paste content and the w/cm were held constant. The results showed the different aggregate proportions, the maximum nominal aggregate sizes, and combinations of different aggregates all had an impact on the performance in the strength, slump, and box test.

Iowa Development of Roller Compacted Concrete, HR-300, 1989

Roller compacted concrete (RCC) is a zero slump portland cement concrete mixture that has been used since the early 1970's in massive concrete structures. Iowa Highway Research Board project HR-300 was established to determine if this type mix could be used to pave roads on the Iowa road system. Manatt's Inc. of Brooklyn, Iowa agreed to pave an 800 ft. x 22 ft. x 10 in. section of RCC pavement in their Ames construction yard. This report discusses the construction of the test slab and interprets test results conducted during and after construction. It was observed that RCC can be placed with conventional asphalt paving equipment. However, there are several problems with RCC paving which must be resolved before RCC can become a viable paving alternative on Iowa's roadway system.

Effect of Mix Times on PCC Properties, HR-1066, 1998

The objectives of this research were the collection and evaluation of the data pertaining to the importance of concrete mixing time on air content and distribution, consolidation and workability for pavement construction. American Society for Testing and Materials (ASTM) standard C 94 was used to determine the significance of the mixing time on the consistency of the mix being delivered and placed on grade. Measurements of unit weight, slump, air content, retained coarse aggregate and compressive strength were used to compare the consistency of the mix in the hauling unit at the point of mixing and at the point placement. An analysis of variance was performed on the data collected from the field tests. Results were used to establish the relationship between selected mixing time and the portland cement concrete properties tested. The results were also used to define the effect of testing location (center and side of truck, and on the grade) on the concrete properties. Compressive strength test concepts were used to analyze the hardened concrete pavement strength. Cores were obtained at various locations on each project on or between vibrator locations to evaluate the variance in each sample, between locations, and mixing times. A low-vacuum scanning electron microscope (SEM) was used to study air void parameters in the concrete cores. Combining the data from these analysis thickness measurements and ride in Iowa will provide a foundation for the formulation of a performance based matrix. Analysis of the air voids in the hardened concrete provides a description of the dispersion of the cemtitious materials (specifically flyash) and air void characteristics in the pavement. Air void characteristics measured included size, shape and distribution.

Development of an Economic Dust Palliative for Limestone Surfaced Secondary Roads, HR-297, 1990

This research project was directed at laboratory and field evaluation of sodium montmorillonite clay (bentonite) as a dust palliative for limestone surfaced secondary roads. It had been postulated that the electrically charged surfaces of the clay particles could interact with the charged surfaces of the limestone and act as a bonding agent to agglomerate fine (-#200) particulates and also to band the fine particulates to larger (+#200) limestone particles. Laboratory testing using soda ash dispersed bentonite treatment of limestone fines indicated significant improvement of compressive strength and slaking characteristics. It was recommended that the project proceed to field trials and test roads were constructed in Dallas and Adair counties in Iowa. Soda ash dispersed bentonite solutions can be field mixed and applied with conventional spray distribution equipment. A maximum of 1.5% bentonite(by weight of aggregate)can be applied at one time. Higher applications would have to be staged allowing the excess moisture to evaporate between applications. Construction of higher application treatments can be accomplished by adding dry bentonite to the surfacing material and then by dry road mixing. The soda ash water solution can then be spray applied and the treated surfacing material wet mixed by motor graders to a consistency of 3 to 4 inch slump concrete. Two motor graders working in tandem can provide rapid mixing for both methods of construction. Calcium and magnesium chloride treatments are 2 to 3 times more effective in dust reduction in the short term (3-4 months) but are prone to washboarding and potholing due to maintenance restrictions. Bentonite treatment at the 2-3% level is estimated to provide a 30-40% dust reduction over the long term(18-24 months). Normal maintenance blading operations can be used on bentonite treated areas. Vehicle braking characteristics are not adversely affected up to the 3.0% treatment level. The bentonite appears to be functioning as a banding agent to bind small particulates to larger particles and is acting to agglomerate fine particles of limestone. This bonding capability appears recoverable from environmental effects of winter, and from alternating wet and dry periods. The bentonite appears to be able to interact with new applications of limestone maintenance material and maintains a dust reduction capability. Soda ash dispersed bentonite treatment is approximately 10 times more cost effective per percent dust reduction than conventional chloride treatments with respect to time. However,the disadvantage is that there is not the initial dramatic reduction in dust generation as with the chloride treatment. Although dust is reduced 30-40% after treatment there is still dust being generated and the traveling public or residents may not perceive the reduction.

Bentonite Treatment for Economical Dust Reduction on Limestone Surfaced Secondary Roads, HR-351, 1995

This research project was directed at laboratory and field evaluation of sodium montmorillonite clay (Bentonite) as a dust palliative for limestone surfaced secondary roads. It was postulated that the electrically charged surfaces (negative) of the clay particles could interact with the charged surfaces (positive) of the limestone and act as a bonding agent to agglomerate fine (-#200) particulates, and also to bond the fine particulates to larger (+#200) limestone particles. One mile test roads were constructed in Tama, Appanoose, and Hancock counties in Iowa using Bentonite treatment levels (by weight of aggregate) ranging from 3.0 to 12.0%. Construction was accomplished by adding dry Bentonite to the surfacing material and then dry road mixing. The soda ash/water solution (dispersing agent) was spray applied and the treated surfacing material wet mixed by motor graders to a consistency of 2 to 3 inch slump concrete. Two motor graders working in tandem provided rapid mixing. Following wet mixing the material was surface spread and compacted by local traffic. Quantitative and qualitative periodic evaluations and testing of the test roads was conducted with respect to dust generation, crust development, roughness, and braking characteristics. As the Bentonite treatment level increased dust generation decreased. From a cost/benefit standpoint, an optimum level of treatment is about 8% (by weight of aggregate). For roads with light traffic, one application at this treatment level resulted in a 60-70% average dust reduction in the first season, 40-50% in the second season, and 20-30% in the third season. Crust development was rated at two times better than untreated control sections. No discernible trend was evident with respect to roughness. There was no evident difference in any of the test sections with respect to braking distance and braking handling characteristics, under wet surface conditions compared to the control sections. Chloride treatments are more effective in dust reduction in the short term (3-4 months). Bentonite treatment is capable of dust reduction over the long term (2-3 seasons). Normal maintenance blading operations can be used on Bentonite treated areas. Soda ash dispersed Bentonite treatment is estimated to be more than twice as cost effective per percent dust reduction than conventional chloride treatments, with respect to time. However, the disadvantage is that there is not the initial dramatic reduction in dust generation as with the chloride treatment. Although dust is reduced significantly after treatment there is still dust being generated. Video evidence indicates that the dust cloud in the Bentonite treated sections does not rise as high, or spread as wide as the cloud in the untreated section. It also settles faster than the cloud in the untreated section. This is considered important for driving safety of following traffic, and for nuisance dust invasion of residences and residential areas. The Bentonite appears to be functioning as a bonding agent.

Non-Grouted Bonded PCC Overlay City of Oskaloosa, HR-528, 1993

Based upon the success the Iowa Department of Transportation has had using thin bonded, low slump, dense portland cement concrete on bridge decks for rehabilitation, it was decided to pursue research in the area of bonded portland cement concrete resurfacing of pavements. Since that time, in an effort to reduce costs, research was conducted into eliminating the grouting operation. On this project a non-grouted overlay was used to modernize an existing urban street. This research project is located in the City of Oskaloosa on 11th Avenue from South M Street to South Market Street. Construction of the project went well and the non-grouted overlay has performed very well to date.

An Evaluation of Concrete Bridge Deck Surfacing in Iowa (with corrections), MLR-75-1, 1975

Iowa has been using low slump concrete for repair and surfacing of deteriorated bridge decks on a routine basis since the mid 1960'2. More than 150 bridges have been resurfaced by this method with good results. A study was initiated in 1973 to evaluate 15 bridges resurfaced with low slump concrete, and one bridge resurfaced with latex modified concrete. The evaluation includes an assessment of concrete physical properties, chloride penetration rates, concrete consolidation, and riding qualities of the finished bridge deck. Results indicate that the overall properties of these two types of concrete are quite similar and have resulted in a contractor option concerning which system shall be used on bridge deck repair/resurfacing projects.

Performance Based Specifications, TR-403, 1998

The goal in highway construction and operation has shifted from method based specifications to specifications relating desired performance attributes to materials, mix designs, and construction methods. Shifting from method specifications to performance based specifications can work as an incentive or disincentive for the contractor to improve performance or extend pavement life. This literature search was directed at a review of existing portland cement concrete performance specification development, and the criteria that can effectively measure pavement performance. The criteria identified in the literature include concrete strength, slab thickness, air content, initial smoothness, water-cement ratio, unit weight, and slump. A description of each criterion, along with the advantages, disadvantages, and test methods for each are identified. Also included are the results from a survey that was sent out to various state, federal, and trade agencies. The responses indicated that 53% currently use or are developing a performance based specification program. Of the 47% of agencies that do not use a performance based specification program, over 34% indicated that they would consider a similar program. The most commonly measured characteristics include thickness, strength, smoothness, and air content. Lastly recommendations and conclusions are made regarding other factors that affect pavement performance and a proposed second phase of the research is suggested. The research team suggests that a regional expert task group be formed to identify performance levels and criteria. The results of that effort will guide the research team in the development of new or revised specifications.