Volume Of Air Voids Research Articles

Factors influencing the wetting performance of asphalt emulsion on RAP surface

The wetting performance of asphalt emulsion on reclaimed asphalt pavement (RAP) strongly affects the physical bonding ability of asphalt emulsion-RAP interface. For a more comprehensive understanding on the wetting performance of asphalt emulsion on RAP, many factors affecting the wetting performance of asphalt emulsion on RAP are studied, including the asphalt and emulsifier dosage in asphalt emulsion, RAP asphalt aged degree, and some additives (such as wetting agent, hydrated lime and silane coupling agent). The contact angle of asphalt emulsion on RAP asphalt surface and the other wetting parameters calculated by the surface wetting theory were used to comprehensively analyze the wetting performance. The results show that all of the tested factors have influence on the wetting performance of asphalt emulsions. The grey relational analysis indicates that the wetting agent, hydrated lime and silane coupling agent have significant effects on the wetting performance of asphalt emulsion on RAP. A suitable dosage of wetting agent, hydrated lime modified with silane coupling agent (HL-SCA) can decrease the contact angle and improve the wetting speed of asphalt emulsion on RAP. Meanwhile, the addition of both wetting agent and hydrated lime modified with silane coupling agent can greatly decrease the volume of air voids and improve the indirect tensile strength of cold recycled mixture with asphalt emulsion. Therefore, the wetting agent and the HL-SCA are recommended to improve the wetting performance of asphalt emulsion on RAP and the mechanical performance of cold recycled mixture with asphalt emulsion.

Functional and structural assessment of an experimental section gap graded modified with sugarcane bagasse ash

Gap-graded aggregate combined with asphalt rubber presents a high-performance alternative for roads with heavy traffic loads, offering advantages over conventional mixtures in terms of permanent deformation (rutting), fatigue life, and texture. In this study, the conventional filler in the well-established mixture was substituted with sugarcane bagasse bottom ash (SCBA) at a proportion of 5% of the total mineral aggregates. The objective was to enhance the mechanical performance of the asphalt coating while ensuring proper disposal of this waste material. Compared to conventional filler, SCBA is less dense, has smaller dimensions, and exhibits greater roughness, thereby affecting the volumetric parameters of the Marshall mix design. Consequently, the volume of voids in mineral aggregates and voids filled with asphalt increased while maintaining the same volume of air voids (5.3%). Consequently, there was a notable increase in Marshall Stability (40%) and Indirect Tensile Test (22%) mechanical parameters. Following laboratory analysis, the modified mixtures were applied as asphalt coating on a high-traffic highway (BR-158). Field specimens revealed an 18% increase in the Resilience Modulus (4088 MPa; 3478 MPa). Additionally, its Flow Number exhibited a 73% increase (16,707; 9681), and its permanent deformation rate was 28% lower within 10,000 cycles in the dynamic creep test. This was further supported by an 11% reduction in permanent deformation rate in the Hamburg Wheel Tracking Device (HWTD) within 20,000 cycles (3.2 mm; 3.6 mm). In conclusion, the partial replacement of conventional filler with sugarcane bagasse ash within the established granulometric range has demonstrated technical feasibility both in laboratory and field settings.

Design and Application of Rich Bottom Layer Mixtures

This study aims to summarize design indexes for rich bottom layer mixtures (RBLMs) and design asphalt mixtures with superior performance to reduce reflective cracks and fatigue cracking resulting from semi-rigid base cracking in the asphalt layer. First, this study synthesizes the research results about RBLMs and introduces the related design indexes. After that, using ABAQUS 6.13, finite element analysis was performed to analyze the change in bottom stress when the base cracked and the interlayer bond weakened. SBS-modified asphalt mixtures (SMMs) and composite-modified asphalt mixtures (CMMs) were subsequently developed as RBLMs utilizing the Marshall test method and applied on a test road. The research findings reveal that design indexes for RBLMs include a volume of air voids (VVs) within the range of 2.0–3.0%, a maximum flexural strain exceeding 3500με, and a dynamic stability surpassing 1000 cycles/mm. Both mixtures satisfy the design requirements, with the CMM demonstrating superior performance and offering promising application prospects. Future research endeavors will concentrate on prolonged monitoring of the test section to authenticate the effectiveness of an RBL in practical road applications.

Proposed automated contrast-enhanced microscopical method for evaluating air void structure in compacted asphalt concrete mixtures

There is no direct, less expensive, and practical method to measure the interconnectivity and parameters of air voids in asphalt mixtures other than the total air void volume calculated traditionally using bulk and maximum theoretical specific gravities. Unlike the conventional method, this paper proposes a method that is suitable for advanced applications and studies, such as for the evaluation of air void distribution and air void gradient to model and simulate long-term aging, predict top-down fatigue cracking, evaluate the effectiveness of compaction of thick lifts, and satisfy the representative volume element (RVE) requirements (a homogenous and representative specimen) for performance tests. Developing the proposed compact asphalt evaluation method included modifying the sample preparation methods and analysis from the American Society of Testing & Materials (ASTM), C457 Method C, and recently applied in the analyses of two independent studies at the Federal Highway Administration (FHWA). The first study was focused on checking the air void distribution within the small specimen for dynamic modulus and uniaxial cyclic fatigue tests using AASHTO TP 132 and TP 133, respectively. Results of air void analyses conducted on the interior and exterior sides of several slices sawn from different compacted asphalt mixtures consistently showed that the air void contents on the external sides are higher than on the interior. The second study was to evaluate whether the thicker-than-typical lift thickness to nominal maximum aggregate (NMAS) ratio was causing any top-to-bottom air void gradient in the pavement. Results showed that air void sizes and contents are consistently higher along the top ends of all the cores, and the total air void contents measured using the new method on several specimens from the field were comparable with the indirectly calculated air void percent with up to ± 0.4 percent random error. Overall, the new method is practical to apply to larger-size samples and is a tool that both agencies and contractors can use for confirming in situ void uniformity. Its application can support innovations and improve performance in asphalt pavement construction.

Effect of Poly(ethylene glycol)–Poly(propylene glycol) Triblock Copolymers on Autogenous Shrinkage and Properties of Cement Pastes

This study investigates the hydration, microstructure, autogenous shrinkage, electrical resistivity, and mechanical properties of Portland cement pastes modified with PEG-PPG triblock copolymers with varied molecular weights. The early age properties including setting time and hydration heat were examined using the Vicat test and isothermal calorimetry. The hydration products and pore size distribution were analyzed using thermogravimetric analysis (TGA) and nitrogen adsorption, respectively. Mechanical properties and electrical resistivity were evaluated using the compressive strength test and electrochemical impedance spectroscopy (EIS). It was shown that the addition of the copolymers reduced the surface tension of the cement paste pore solution due to the presence of a hydrophobic block (PPG) in the molecular structure of the copolymers. The setting time and hydration heat were relatively similar in the control paste as well as the pastes modified with the copolymers. The results showed that copolymers were able to reduce the autogenous shrinkage in the paste due primarily to a reduction in pore solution surface tension. TGA showed a slight increase in the hydration degree of the paste modified with the copolymers. The compressive strength was reduced in the pastes modified with the copolymers that showed an increased volume of air voids. The addition of copolymers did not affect the electrical resistivity of the pastes except in the case where there was a large volume of air voids, which acted as electrical insulators.

Investigation on alkali-activated insulation mortar containing high-volume recycled concrete powder for energy-efficient buildings

The influence of recycled concrete powder (RCP) on the thermal insulation of alkali-activated materials remains unclear. Hence, this study develops an innovative alkali-activated insulation mortar, serving RCP and blast furnace slag as the precursor and expanded polystyrene (EPS) beads as fine aggregate, together with air entrainer. Experimental results show that the mortar had satisfactory workability owing to the RCP substitution, supported by appearance and infrared thermal imaging tests. As the ratio increased, the density, compressive strength, and thermal conductivity of the mortar decreased, due to the increasing volume of porous paste and internal air voids. Subsequently, the material design of the mortar was optimized through the adjusted Box-Behnken design. The obtained mortar achieved a high-volume use (61.7 wt%) of RCP, and exhibited an extremely low conductivity (∼0.030 W/(m∙K)) among novel lightweight building materials. Energy simulation further indicates that the optimized mortar can surpass traditional insulation materials, including EPS, polyurethane, and rock wool panels, in reducing air conditioning energy consumption across all seasons and climate zones. This was particularly evident in colder cities such as Harbin and Lhasa. Given that increasing the thermal resistance of the envelope can effectively reduce building energy consumption, the development of such sustainable alkali-activated insulation mortar would undoubtedly contribute to the implementation of energy-efficient buildings.

Near‐Nozzle Mixing for Additive Manufacturing of Cementitious Mortar: A Homogeneity Study

AbstractThis paper investigates the Near‐nozzle Mixing (NNM) technique for 3D printing cementitious mortar, focusing on achieving continuous and homogeneous material properties. The NNM's ability to print Natural Sand Mortar (NSM), Recycled Aggregate Mortar (RAM), and Lightweight Mortar (LWM) was assessed. Fresh and hardened properties of each mortar were examined, emphasizing standard deviation (STD) and coefficient of variation (CV) to measure material homogeneity. Fresh properties included slump flow, yield stress, air void volume, density, and water‐to‐cement ratio, while hardened properties covered compressive strength, flexural strength, hardened density, and thermal conductivity. Results showed low CV values for all mortar types, indicating high consistency and homogeneity. NNM showed is capability to print of various materials with customized properties. NSM showed the highest compressive strength, RAM balanced strength and sustainability, and LWM provided the best thermal insulation. The study highlights NNM's versatility and potential for construction applications requiring tailored properties, proving it a promising additive manufacturing solution. The research serves as a foundation for future studies on graded multi‐material printing.

Scouring erosion resistance of nano-marine concrete under the coupled effect of chloride attack and dry - wet cycles

In order to reveal the improving mechanism associated with different types of nanoparticles under the three-factor coupled effects (scour, dry-wet cycles, and Cl- attack), a laboratory investigation was undertaken to evaluate and compare the influence of nano-SiO2 and nano-Fe3O4 with different content on scouring erosion resistance properties of marine concrete. The micro-structure of the interface transition zone (ITZ) in marine-concrete, as well as the features of hydration products, were characterized using advanced techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), differential thermal gravimetric (DTG-DSC) analysis, and mercury intrusion porosimetry (MIP). The test results showed that compressive and flexural strength, as well as scouring erosion resistance of marine-concrete were enhanced with the increasing content of nano-SiO2 and nano-Fe3O4 until the threshold limit of 2%, and performance of NSC20 was better than that of NFC20. Under the three-factor coupling, the strength corrosion resistance coefficient of nano-marine concrete was negatively correlated with the scouring erosion rate and the change rate of scouring erosion area, and positively correlated with the resistivity and the Cl- diffusion coefficient with the increase of corrosion age. When the corrosion age reached 70 days, the average scouring erosion rates of NSC20 and NFC20 were decreased 19.86% and 14.43%, respectively, compared with PC. The convective depth of concrete steadily decreased while its diffusive depth increased relative to concrete without scouring. Cl- binding was increased by 28.5%, 27.2%, and 21.4% for PC, NSC20, and NFC20, respectively. The high chemical activity of nano-SiO2 and nano-Fe3O4 promoted the mechanical performance and durability of concrete through improved density and homogeneity of chlorinated products and optimized the structure of the C-S-H/C-F-H gels in ITZ, as indicated by SEM-EDS observation, XRD, and DTG-DSC analysis. The coupling effects resulted in increasing volume of air voids and micro-cracks, as well as weak ITZ due to SA, which hindered scouring resistance development, as indicated by the MIP analysis.

Mechanical and internal structural damage evolution in cold recycled mixture under fatigue loading

Cold recycling technology has the virtue of lower cost, fewer pollutant emissions, and less consumption of raw materials and fossil fuels in pavement maintenance and construction. This study aimed to investigate the evolution of fatigue damage in cold recycled mixtures and provide a theoretical basis for improving the service life of cold recycled pavements with high reclaimed asphalt pavement (RAP) utilization rates, ultimately contributing to energy and resource conservation. To achieve this objective, we conducted a study on the mechanical and internal structural damage evolution of cold recycled mixtures produced using different agents (cement and asphalt emulsion). This was accomplished by combining indirect tensile fatigue testing with X-ray CT scanning techniques. The results indicate that the mechanical response of cold recycled mixtures under fatigue loading is closely related to the evolution of their internal structure during various stages of fatigue. Furthermore, it is found that the type of stabilization agent used in these mixtures has a significant impact on their initial air void content and volume distribution, which ultimately affects both the rate and extent of their mechanical and structural damage evolution. Based on these results, recommendations have been proposed for enhancing the fatigue performance of cold recycled pavement through appropriate mixture design strategies that account for these factors mentioned above.

Same-day versus delayed simulation imaging after placement of a perirectal hydrogel spacer for prostate radiotherapy.

Placement of a perirectal hydrogel spacer has been demonstrated to reduce the risk of rectal toxicity from prostate radiation. Practices vary regarding the timing of CT simulation after hydrogel placement, and the ideal schedule remains unknown. Thirty patients with localized prostate adenocarcinoma underwent transrectal ultrasound-guided placement of an iodinated SpaceOAR™ hydrogel prior to radiotherapy. Per evolving practice, 15 completed same-day simulation and 15 returned for simulation 1-2 weeks later. Hydrogel volume, perirectal distance, air-void volume, and rectal dosimetry per NRG GU005 were compared between CT simulation, 1st fraction Cone-Beam-CT (CBCT), and final CBCT. CT simulation occurred 8.8 ± 2.4 days after placement in the delayed group, with no significant difference in the interval between simulation and 1st fraction between groups (p = 0.165). Greater observed de-creases in hydrogel volume (0.57 cc vs. 0.04 cc, p = 0.0002), and perirectal distance at both mid-gland (1.32mm vs. 0.17mm) and tallest point (2.40mm vs. 0.04mm) were seen on 1st-fraction CBCT in the same-day group (p = 0.0039; p = 0.0002). Per dosimetry recalculated on 1st fraction CBCT, five (D3 cc and D50%) versus one (D50%) rectal dose parameters were exceeded in the same-day and delayed groups, respectively, and 10 versus one parameters had a relative increase of ≥ 20%. Due to the evolving anatomic changes in the days following hydrogel placement, same-day simulation scanning may introduce unintended variability in rectal dosimetry at the time of prostate radiotherapy.

Utilizing waste latex paint toward improving the performance of concrete

In this paper, incorporating the waste latex paint (WLP) into the conventional concrete as a partial replacement of sand to improve its durability was investigated. The fresh and hardened characterizations, in addition to the durability of concrete, were examined. The slump test was used to evaluate the fresh properties, while the hardened properties were evaluated through the volume of voids and absorption rate, in addition to the compressive, splitting tensile, and flexural strengths tests. The durability performance was evaluated by the surface resistivity, bulk electrical resistivity, as well as freeze and thaw resistance tests. The results showed a reduction in the workability with the addition of WLP, which required high dosages of superplasticizer to maintain the same slump in all the mixtures. Although there was a reduction in the compressive, splitting tensile, and flexural strengths, incorporating the WLP into the OPC concrete improved the durability significantly. Specimens had 5% and 10% of WLP passed the 300 freeze and thaw cycles without deterioration in the relative dynamic modulus of elasticity, compared with the reference mixtures that failed after only 144 cycles. Simultaneously, the surface and bulk electrical resistivity increased by approximately 125% and 138%, respectively, as result of reducing the volume of air voids that was decreased by 9%. The SE images and EDS spectrums showed denser cementitious matrixes with a film of polymeric layer covered the hydration products with adding waste latex paint.

Valorization of waste foundry sand aggregates in hot-mix asphalt

Metal smelting generates a significant volume of industrial solid waste foundry sand (WFS). Although several standards and studies have established practices and requirements for its use, a large portion of the disposed WFS goes to industrial landfills. This study aims to evaluate the value of WFS as an aggregate in hot-mix asphalt mixtures (HMA) using systematic criteria for classification, potentialities, waste generated and applicability. To this end, molding sand (MS) and fine dust of exhaustion (FDE) were characterized, to identify their potential for application as aggregates in asphalt mass. Different contents of MS, FDE, and Blend (BL) were studied according to the normative granulometric ranges of aggregates for HMA. Samples were obtained via the Marshall method to verify important properties for the asphalt mix. Ecotoxicity tests were conducted. The results showed that a composition containing 10 wt% of BL presented an air void volume of 3.3%, a stability of 658 kgf, creep of 2.5 mm, and an indirect tensile strength of 0.93 MPa. From a technical and environmental perspective, a 10 wt% BL content was suitable for recovery into HMA. Lower amounts BL yielded results outside the normative limits. WFS can be recovered and applied as a raw material in HMA.

Vapour transfer in the freezing soils – physical phenomena of the frost heave

Study of the hydraulic conductivity in the freezing soils and the frost heave mechanism started as far as in the 30’s of the last century and even earlier. However explanation of frost heave mechanism with hydraulic conductivity is fundamentally wrong approach which lead
 Study of the hydraulic conductivity in the freezing soils and the frost heave mechanism started as far as in the 30’s of the last century and even earlier. However explanation of frost heave mechanism with hydraulic conductivity is fundamentally wrong approach which leads to the complication in the calculations and the predictions of frost heave. The presented work explains the detailed description of the moisture migration in a gas phase within the freezing porous media and gives the mathematical modelling based on the phase transitions of moister as water–gas–water-ice. The proposed method is based on the thermodynamically and phases equilibrium and allows to determine the speed of the mass transfer in the freezing media. The calculations were shown in an example of the experimental testing data. The obtained results admit the strong relationship of the frost heave and air void volume. They also emphasize the impact of soil density, void ratio and moisture content on the amount of built ice in the freezing zone of the soil.
 s to the complication in the calculations and the predictions of frost heave. The presented work explains the detailed description of the moisture migration in a gas phase within the freezing porous media and gives the mathematical modelling based on the phase transitions of moister as water–gas–water-ice. The proposed method is based on the thermodynamically and phases equilibrium and allows to determine the speed of the mass transfer in the freezing media. The calculations were shown in an example of the experimental testing data. The obtained results admit the strong relationship of the frost heave and air void volume. They also emphasize the impact of soil density, void ratio and moisture content on the amount of built ice in the freezing zone of the soil.

Effect of aggregate gradation and asphalt mix volumetrics on the thermal properties of asphalt concrete

The objective of this study is to investigate the impact of aggregate gradation and Superpave volumetrics on thermal properties of asphalt mixtures. Thirty asphalt concrete specimens with three different Nominal Maximum Aggregate Sizes (NMAS) of 19.0, 12.5 and 9.5 mm and two levels of gradation coarseness: fine gradation (FG) and coarse gradation (CG) were prepared. The Transient Plane Source (TPS) method was used to determine thermal properties. Based on the analyses performed, it was concluded visually that heat transfer is highly dependent on the contact area which, in turn, is related to air void volume. Unlike NMAS, the gradation coarseness (G) has some effect on thermal conductivity (TC) (p-value = 0.008 < 0.05). On the contrary, the NMAS, unlike gradation coarseness, has a significant effect on thermal diffusivity (TD) with a p-value of 0.025. Both gradation coarseness and NMAS have a significant effect on thermal diffusivity (p-value = 0.029 < 0.05) and do not have much effect on specific heat (SH) where p-value is greater than 0.05. Nevertheless, it was noticed that the thermal diffusivity increased linearly with an increase in aggregate size from 85.64 mm2/s to 125.79 mm2/s at 9.5 NMAS FG and 19 mm NMAS FG, respectively. Whereas the specific heat and thermal conductivity increase as the asphalt content (AC) increases. Consequently, the highest average values of thermal conductivity and specific heat are 2 W/m.K and 0.025 M.J/m3. K, respectively, at the highest asphalt content of 6.1%. Multiple linear regression, non-linear regression and deep learning (MLR, NLR and DL) equations were developed. The non-linear regression resulted relatively in the best predictive power of all equations. Finally, larger datasets are needed to predict thermal properties with higher confidence.

Relationship between fine aggregate size and the air void system of six mortars: I. Air void content and diameter distribution

Precisely determining the characteristics of the air void system in cement-based materials is important in material design and freeze-thaw durability evaluation. X-ray computed tomography (XCT) has been used to characterize air void systems, since it is able to measure the 3D spatial arrangement of the voids. Though the factors influencing air void formation and arrangement have been well-studied, the role of fine aggregate size and gradation has mainly been ignored. In this paper, six mortars were prepared with varying sand size distributions and their air void system quantitatively characterized via XCT. The role of sand size distribution and blended proportions were combined via calculation of the fine aggregate specific surface area (SSA). A linear relationship between SSA and global air void volume fraction was observed, with increasing air void volume fraction as SSA increased (and sand size decreased). The 2D circle diameter distribution was derived from 2D analysis of each XCT slice and the 3D sphere diameter distribution was derived from 3D analysis of the stacked 3D XCT microstructure. The distributions for 2D and 3D were calculated from each other using stereological methods and compared with the original experimental results. All three methods used were in reasonable agreement. The air void size distributions obtained via high resolution (small voxel size, small scan volume) and low resolution (large voxel size, large scan volume) XCT scans compared favorably in a compatible air void size range, which illustrates how the problems of differing XCT resolutions can be resolved.

HIGH AIR-VOID VOLUME IMPLICATIONS FOR ASPHALT CONCRETE SERVICE-LIFE AND PRICE PENALTY

In road industry, the construction of asphalt concrete layers is a dynamic process that, if not properly done, will lead to problems compromising the pavement performance. One of the most common problems is poor compaction leading to air-void volume above the maximum acceptable. This study discusses the impact of compaction/density deficiencies and presents an innovative model to calculate the asphalt pavement service-life loss in a simple and objective way, and in line with the road construction managers needs to calculate price penalty for contractors. The model was optimized for dense graded asphalt concrete, that typically has a maximum acceptable air‑void volume between 4% and 7%.

Comparison of the operative time and presence of voids of incremental and bulk-filling techniques on Class II composite restorations.

To compare the operative time and presence of air voids on Class II restorations fabricated by dental practitioners with 1 to 5 years of experience using incremental and bulk-filling techniques. Four techniques were evaluated: incremental, bulk-filling, bulk-filling with heated composite, and snowplow technique. Standardized mandibular first molars with a MOD (mesial, occlusal, and distal) cavity were used. Voluntary operators made two restorations using each technique and the time required for each restoration was recorded. The restorations were scanned by micro-computed tomography to calculate the volume of the restoration occupied by air voids. The "operative time" and "volume of air voids" were analyzed individually by two-way ANOVA and Tukey HSD post hoc (α = .05) for the factors operator and insertion technique. A correlation between "operative time" and "volume of air voids" was evaluated using Pearson coefficient (α = .05). The incremental technique required significantly longer time, yet no differences were observed between the bulk-filling techniques. There were no significant differences between techniques regarding the volume of air voids. A significant, but weak, and inverse linear correlation (P = .0059; r = -.29; r2 = 8.41%) was found between the operative time and volume of air voids. There were no significant differences in the volume of air voids among the evaluated techniques, although bulk-filling techniques required a shorter operative time. Hence, implementing bulk-filling techniques by dental schools and restorative dental practitioners with different levels of expertise may reduce chair time and produce a volume of air voids similar to the incremental technique.

Effect of Various Types of Superplasticisers on Consistency, Viscosity, Structure and Long-Term Strength of Geopolymer Products.

This article presents the results of research on the effect of plasticisers made based on four different compounds—melamine (M), naphthalene (NF), acrylic polymers (AP) and polycarboxylic ethers (PC)—added to the tested mixes in the amount of 2% of the fly ash (FA). The influence of superplasticisers (SPs) on the consistency of the fresh concrete was investigated using a flow table and a penetrometer, and the air voids content was determined by means of a porosimeter. Additionally, the influence of plasticisers on the viscosity of the paste was investigated using a rheometer. Hardened mortar that matured under two different conditions was also tested at elevated and room temperatures. The tested properties were 7-, 28- and 90-days compressive strength and internal microstructure viewed under a microscope. NF had the greatest viscosity-reducing effect while it increased the air void volume in the mix at the same time. The highest early and late strengths were obtained after curing in elevated temperature samples with an acrylic-polymer-based superplasticiser. However, the increased curing temperature of the samples only influenced the early strength results. Its effect was not visible after 90 days. The AP addition also had a significant impact on improving the consistency of the mixture. The addition of plasticisers did not affect the microstructure of the specimens.

Determining the air void efficiency of fresh concrete mixtures with the Sequential air method

The Sequential Air Method (SAM), AASHTO TP 118, is the only test that can quantify the air void volume and spacing in fresh concrete but using the results to design a concrete mixture can be challenging. This work introduces a new tool that uses the outputs from the SAM to determine how different ingredients or changes to the environment impact the volume and spacing of the air void system. This tool is known as the Efficiency Chart. The Efficiency Chart can help producers create more reliable and consistent air void systems that also meet the suggested freeze thaw requirements. The Efficiency Chart is made by using 227 diverse concrete mixtures to establish an upper and lower bound of performance. To show the usefulness of this method several examples are presented to show how different admixtures and cements impact the air void systems. Agreement is shown between the predictions of the Efficiency Chart and the results from a hardened air void analysis (ASTM C457). Because the SAM can evaluate fresh concrete, the concrete industry can use the Efficiency Chart to help design and troubleshoot the air void systems in their concrete mixtures.

Mechanisms underlying the strength enhancement of UHPC modified with nano-SiO2 and nano-CaCO3

The unique physical and chemical properties of nano-particles can enhance the nature of cement-based materials at the micro-scale and nano-scale levels, leading to improved properties. To uncover the strengthening mechanism associated with various types of nano-particles, a laboratory investigation was undertaken to evaluate and compare the influence of nano-SiO2 and nano-CaCO3 on mechanical properties of ultra-high performance concrete (UHPC) made with 2% steel fibers. Each type of nano-particle was incorporated at four contents, and the mini-slump flow of the UHPC was maintained at 240–260 mm. The microstructure of the matrix and the fiber-matrix interface of UHPC, as well as the features of hydration products were characterized using advanced techniques, such as electron microscopy (SEM), X-ray diffraction (XRD), differential thermal gravimetric (DTG) analyses, 3D micro-tomography, and mercury intrusion porosimetry (MIP). Test results indicate that both the fiber-matrix strength and mechanical strength of UHPC increased with the increase of nano-SiO2 and nano-CaCO3 until threshold limits of 1% and 3.2%, respectively. The 28-d fiber-matrix bond, compressive, and flexural strengths of the optimal UHPC mixtures made with 3.2% nano-CaCO3 were approximately 40%, 10%, and 20%, respectively, greater than those of the reference mixture. These strength values were higher than those of UHPC made with 1% nano-SiO2. When used below these optimal nano-material contents, the filler and nucleation effects related of the nano-SiO2 and nano-CaCO3 promoted the strength development through improved density and homogeneity with optimized structure of hydration products, as indicated by SEM observation and DTG analysis. Beyond these limits, additional use of nano-materials resulted in increased volume of air voids and capillary pores and weak interfacial zones due to the agglomeration of nano-particles, which hindered strength development.