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International Concrete Abstracts Portal

Showing 1-10 of 793 Abstracts search results

Document: 

SP-338_02

Date: 

March 1, 2020

Author(s):

Kenneth C. Hover

Publication:

Symposium Papers

Volume:

338

Abstract:

PCA researchers interested in the problem of evaporation of bleed water from concrete surfaces borrowed an equation developed by hydrologists to predict evaporation from Lake Hefner in Oklahoma. PCA’s graphical representation of that equation, subsequently modified to its present form by NRMCA, was later incorporated into multiple ACI documents, and is known by concrete technologists world-wide as the “Evaporation Rate Nomograph.” The most appropriate use of this formulation in concrete construction is to estimate the evaporative potential of atmospheric conditions (known as “evaporativity”). Since the difference between actual and estimated evaporation rate can be in the range of ± 40% of the estimate, best use of the equation as routinely applied is as a semi-quantitative guide to estimate risk of early drying and inform decisions about timing and conduct of concrete placing and finishing operations. Use of the “Nomograph” and related “Apps” in specifications is more problematic, however, given: 1.) the inherent uncertainty in its underlying equation, 2.) the difficulty in obtaining input data that appropriately characterize jobsite microclimate, and 3.) establishing a mixture-specific criterion for tolerable evaporation rate.


Document: 

SP-336_05

Date: 

December 11, 2019

Author(s):

Lisa E. Burris, Prasanth Alapati, Kimberly E. Kurtis, Amir Hajibabaee, M. Tyler Ley

Publication:

Symposium Papers

Volume:

336

Abstract:

Cement production is one of the largest contributors to CO2 emissions in the U.S. One method of reducing emissions associated with concrete is through usage of alternative cements (ACMs). Some of the more common ACMs include calcium sulfoaluminate cement, calcium aluminate cement, ternary calcium aluminate-calcium sulfate-portland cements, and chemicallyactivated binders, all of which have been shown to have lower carbon footprints than ordinary portland cement (OPC). However, the durability, and more specifically, the shrinkage behavior, of these cements has not been adequately examined, and must be better understood and able to be controlled before ACM concrete can be effectively used in the field. As a first step in increase understanding of shrinkage in ACMs, this paper examines chemical, autogenous, and drying shrinkage in the ACMs listed above. Results show that, despite greater quantities of chemical shrinkage, CSA, CAC, and chemically activated fly ash binder undergo less autogenous and drying shrinkage than OPC.


Document: 

SP-334-09

Date: 

September 30, 2019

Author(s):

Ruizhe Si, Qingli Dai, and Jiaqing Wang

Publication:

Symposium Papers

Volume:

334

Abstract:

The fresh and mechanical properties as well as the durability of the polyvinyl alcohol (PVA) fiber-reinforced rubber mortar were evaluated in this study. The mini-slump test showed that the workability of the cement mortar was decreased with the both added rubber aggregates and PVA fibers. The mechanical strength was reduced in rubberized mortar compared with the plain cement mortar. The added PVA fiber with optimized content improved the compressive strength of the rubberized mortar. The ultrasonic wave velocity test showed that the dynamic modulus of the rubberized mortar was lower than that of plain mortar. In addition, the fiber reinforcement can enhance dynamic modulus (shown as the increased ultrasonic wave velocity) in the rubberized mortar mixtures. The drying shrinkage of the cement mortar was reduced by using the low content of the rubber aggregate as well as applying the PVA fiber reinforcement.


Document: 

SP-334-08

Date: 

September 30, 2019

Author(s):

Yasser Khodair, Arif Iqbal, and Mohammed Hussaini

Publication:

Symposium Papers

Volume:

334

Abstract:

This study discusses the results of an experimental program conducted to study the fresh, hardened and unrestrained shrinkage characteristics of self-consolidating concrete (SCC) using fine recycled asphalt pavement (FRAP) and high volume of supplementary cementitious materials (SCMs) including class C fly-ash (FA) and slag (S). Sixteen mixtures were prepared with different percentages of FA, S, and FRAP. SCC mixtures were divided into four groups where each group had a different percentage of FRAP replacing fine aggregate (10%, 20%, 30%, 40%) and Portland cement being replaced by different percentages of SCMs. The water to cementitious material (w/cm) ratio of 0.4 was used for SCC mixtures with a target slump flow higher than 500 mm. The flowability, deformability, filling capacity and resistance to segregation were measured to determine the fresh properties of the mixtures. Moreover, the compressive strength at 14, 28, and 90 days and split tensile strength at 28 days were determined and durability characteristics including unrestrained shrinkage up to 90 days were tested. Analysis of experimental data showed that most of the mixtures satisfied the SCC fresh properties requirements. The addition of FRAP had an adverse effect on the compressive, tensile strength and unrestrained free shrinkage of SCC mixtures.


Document: 

SP-335_01

Date: 

September 20, 2019

Author(s):

Joshua Hogancamp, Cesario Tavares, and Zachary Grasley

Publication:

Symposium Papers

Volume:

335

Abstract:

The current state of the art in fiber-reinforced cement-based materials indicates that adding multiple fiber types or sizes primarily creates a superpositioned behavior state: the behavior from each fiber type separately is added to the composite behavior of the material. Carbon nanofibers (CNFs) and milled carbon microfibers (MCMFs) can increase cracking resistance in cement-based materials by bridging cracks, although CNFs bridge cracks significantly smaller than cracks bridged by MCMFs. This research suggests that multi-scale fiber reinforcement (CNFs with MCMFs) might add compounded benefits to cracking resistance. Tests evaluating cracking resistance were performed utilizing a restrained-ring drying shrinkage test with Portland cement mortars. The CNFs and/or MCMFs were pre-mixed with cement using a sonication/distillation technique and/or rotary tumbling. Concentrations of CNFs and MCMFs were tested up to 5% and 6% by mass of cement, respectively. Restrained ring tests on mortar with high concentrations of CNFs or MCMFs reveal delayed cracking time by factors up to 6.4 or 2.6, respectively. Combining CNFs with MCMFs delayed cracking by a factor of at least 52. The increase in cracking resistance is attributed to the combined effects of bridging cracks of multiple sizes.


Document: 

SP-335_07

Date: 

September 20, 2019

Author(s):

Xin Wang and Kejin Wang

Publication:

Symposium Papers

Volume:

335

Abstract:

In this work, effects of nanosilica (NS), nanolimestone (NL), and nanoclay (NC) additions on hydration and strength of cement pastes were studied. The pastes were made with Type I ordinary Portland cement (OPC), 0 and 30% Class F fly ash (FA), and 0 or 1% nanomaterials. All pastes had a water-to-binder ratio of 0.5. Chemical shrinkage was monitored as an indication of cement hydration process. X-ray diffraction (XRD) was conducted to identify crystalline hydration products. Thermogravimetric analysis (TGA) was used to quantify calcium hydroxide (CH) and chemically bound water. The results indicate that the rate of chemical shrinkage curve can be divided into five stages, similar to that observed from the rate of cement hydration curve measured from a calorimetry test. All nanomaterials increased the rate of chemical shrinkage associated with C3S and C2S reactions; but different types of nanomaterials had different effects on the rate of chemical shrinkage associated with secondary C3A reaction. All nanomaterials improved strength of OPC paste at ages up to 28 days; but the improvement was not clear for OPCFA pastes. Through reaction with OPC and FA, NL stabilized voluminous ettringite and produced hemicarbonate (Hc) instead of less voluminous monosulfate (Ms).


Document: 

SP-329-23

Date: 

September 26, 2018

Author(s):

Fei Xiao, Yongwei Wang, Jinhuan Lv, Jie Zhang, and Tongwei Lu

Publication:

Symposium Papers

Volume:

329

Abstract:

In many parts of the world, the lowest temperature in winter is less than -20 degrees Celsius. It is an important problem in the field of construction engineering to improve the quality of concrete engineering and improve the durability of the structure under extreme climate. This paper introduces the development of ultralow temperature anti freezing pumping admixture. In the experiment, the concrete cured at -4°F (-20 °C) or -13°F (-25°C) for 7 days. And then the specimens were maintained in standard condition for different ages. Mechanical and durability properties of concrete were test in different curing conditions and different ages were studied. Mechanical properties include “negative temperature” compressive and flexural strength. Durability includes anti-permeability performance, dry shrinkage and chloride ion penetration resistance. The experimental data shows that the concrete have good mechanical and durability properties in ultra-low temperature because of the addition of an anti-freezing pumping agent. Compared with ordinary antifreeze, the negative temperature strength of concrete mixed with this ultralow temperature anti freezing pumping agent can be increased by more than 100%. By means of scanning electron microscopy (SEM) and pore size analysis were carried out. The action of this super low temperature anti freezing pumping agent and the frost resistance mechanism of concrete are analyzed.


Document: 

SP-330-10

Date: 

September 26, 2018

Author(s):

Luigi Coppola, Denny Coffetti, and Elena Crotti

Publication:

Symposium Papers

Volume:

330

Abstract:

Since replacement of portland cement by other cementations materials is one of the main strategies to reduce the environmental impact of cementitious mixture, several innovative portland-free binders have been investigated. This paper is aimed to study a ground granulated blast furnace slag (precursor) activated with a mixture in powder form (activator) of sodium metasilicate pentahydrate, potassium hydroxide and sodium carbonate to manufacture portland-free mortars for conservation, restoration and retrofitting of existing masonry buildings and concrete structures. Several activator/precursor combinations (2%-32% by mass) were used to investigate the effect of alkali activation on the rheological, elastic and physical performances of repair mortars. The experimental data show that by changing the activator/precursor combination it is possible to “tailor” the 28-day compressive strength of the mortar. The activator dosage represents the key parameter influencing not only mechanical performance but also the hydraulic shrinkage: the higher the activator dosage, the more pronounced the mortar shrinkage. Shrinkage values for alkali-activated mortars (AAM) are significantly higher (2000 – 4000 ∙ 10-6) compared with those of cement-based mortars with the same compressive strength. Consequently, a reduction of shrinkage by means of shrinkage reducing (SRA) and/or water retention admixtures is necessary. However, although shrinkage is very high, the modulus of elasticity is about 40% lower than that of a portland cement mortar of the same strength level. On the basis of the experimental data AAMs seem to be more promising for a sustainable future in construction since the GER (Gross Energy Requirement) and GWP (Global Warming Potential) are dramatically reduced by 80 - 90% and 70 - 80%, respectively compared with traditional portland cement mortars with the same compressive strength.


Document: 

SP-330-08

Date: 

September 26, 2018

Author(s):

Ivan Janotka, Pavel Martauz, and Michal Bacuvcik

Publication:

Symposium Papers

Volume:

330

Abstract:

Hybrid cement (H-CEMENT) is an innovative cement of the producer from Slovakia. H-CEMENT is suitable for the production of ready-mixed concrete of compressive strength classes up to C 30/37 (4350/5370 psi) along with shrinkage-reducing and alkali-aggregate reaction-mitigating properties. The results of 5-years of exposure of H-CEMENT mortar in an aggressive sulfate solution are compared with two reference cement mortars made either with CEM I or sulfate-resistant CEM I SR 0. Sulfate resistance of H-CEMENT was evaluated in the regularly-renewed aggressive 5% solution by none-destructive tests (dynamic modulus of elasticity and length changes), destructive tests (flexural and compressive strength), microstructure studies (XRD, TG-DTA and SEM), wet chemical analyses (mainly the estimation of SO3 content), and pore structure technique (MIP). The results give evidence of the same high sulfate resistance for H-CEMENT as that for CEM I SR 0 with C3A = 0.


Document: 

SP-329-28

Date: 

September 26, 2018

Author(s):

Nanxiao Gao, Qianping Ran, and Min Qiao

Publication:

Symposium Papers

Volume:

329

Abstract:

The shrinkage of concrete can adversely affect not only its fitness for use, but also the durability of concrete structural elements. Compared with traditional PCEs, shrinkage-reducing polycarboxylate superplasticizer (SR-PCE) can decrease the concrete shrinkage. Therefore, it’s a new way to increase the durability of concrete in recent years. In this paper, three novel SR-PCEs were designed and synthesized by the free radical copolymerization of acrylic acid and the macromonomers with hydrophobic poly(ethylene oxide and/orpropylene oxide)-based side chains.The effect of the side chain hydrophobicity on drying shrinkage and dispersion performance for concrete was investigated, and the relationship between side chainhydrophobicity, drying shrinkage and pore solution properties (surface tension and alkali ions concentration)was also studied. Based on these investigations, a new kind of SR-PCE was developed (SR-PCE3). Upon the addition of 0.4% SR-PCE3, the water-reducing rate was about 21.4% and the drying shrinkage of concrete was decreased by 24.0% at 60 days. Introducing hydrophobic group as the side chain into the polymer may be an effective way to change the properties of pore solution significantly with low concentration of SR-PCE and thus solve the contradiction between adsorption dispersing and shrinkage reducing.


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