Long-term Properties Of Concrete Research Articles

Influence of printing parameters on the durability of 3D-printed limestone calcined clay cement mortar: overlap between filaments and nozzle offset

Large-scale cement-based Additive Manufacturing (AM), also known as 3D Concrete Printing (3DCP), is a promising technique to innovate the construction industry. The durability properties of printed specimens have been studied and compared to those of cast samples in the literature. However, no study has evaluated and quantified the influence of printing parameters on the durability of 3DCP specimens. Aspects such as nozzle offset and the overlap between printed filaments, among others, may influence the porosity of the samples and, therefore, the durability properties. This paper aims to investigate the influence of printing parameters on the durability of 3D manufactured mortar samples. The effects of the printing height and overlap between filaments on the durability properties were analysed in the X, Y and Z axes. An experimental investigation of 39 samples was conducted. Printed and cast specimens were subjected to a curing process for up to 90 days in a water tank at a temperature of 20 °C. Durability tests (oxygen permeability, electrical resistivity, and porosity) were performed at 7, 28 and 90 days. Relationships between the printing variables and durability properties with time were derived. Based on this study, it is concluded that the long-term properties of concrete are significantly sensitive to the overlap between filaments and the nozzle offset. In general, the durability properties were enhanced by modifying the printing parameters. In particular, an overlap of 4 mm showed the most promising results in this regard.

Analytical Study on Time-Dependent Stiffness of Stud Shear Connectors

Concrete creep weakens the spring stiffness of stud shear connectors (SSCs) and increases the long-term deflection of long-span composite beams. The time-dependent properties of SSC are of great importance for the long-term evaluation of composite steel construction. This paper proposes the time-dependent stiffness (TDS) method based on the analytical solution of the beam on a viscoelastic foundation to simulate the SSC under the sustained push-out load. TDS method combines beam theory and the viscoelastic property of hardened concrete. The long-term slip of SSC is predicted by hand calculation of the explicitly expressed governing equation, and it is close to the refined finite element analysis (FEA) results. The constants and parameters used to determine TDS seem to be insensitive regarding geometric and material variation. TDS may provide a simplified method to incorporate the time-dependent partial interaction into complex composite structures by saving the consumption of computer storage and advanced modeling time which are usually required in the refined modeling at the steel-concrete interface, especially when the long-term properties of concrete are of interest.

Effects of different composite mineral admixtures on the early hydration and long-term properties of cement-based materials: A comparative study

The exploration of sustainable and green cement-based materials prepared from industrial solid wastes is an important research direction in the development of new building materials. This paper carried out a quantitative comparative study of the influences of different composite mineral admixtures prepared with fly ash, steel slag, and ground granulated blast furnace slag (GBFS) as supplementary cementitious materials (SCMs) on the early hydration, long-term (360 d and 720 d) mechanical properties and penetrability of cement-based systems. The results show that adding GBFS and steel slag has the greatest influence on the early hydration of cement due to their synergistic reactions. Over time, it becomes increasingly apparent that adding composite admixtures containing GBFS and fly ash can refine the long-term pore structure, reduce the brittleness, improve the long-term strength and chloride ion penetrability resistance of concrete to the greatest extent. However, adding composite admixtures containing steel slag and fly ash has no positive impact on the long-term properties of concrete. From a comprehensive perspective, considering early hydration, long-term properties and economic costs, composite admixtures containing GBFS and steel slag have potential for wide popularization and applications which can promote the sustainable utilization of steel slag and cleaner production of green concrete.

The Effect of a High Amount of Micro-Fillers on the Long-Term Properties of Concrete.

Concretes in which a large portion of fine natural aggregate is replaced with inert mineral powders would offer both economic and ecological benefits for the concrete industry, and they represent eco-friendly materials. Moreover, using the powders having potential pozzolanic effect could have positive extra effect on the properties of concrete. This paper analyses the impact of a high dosage of three kinds of micro-fillers (brick, concrete and glass powders) on the properties of concrete over a three-year period. Microfillers were applied as 40% replacement of 0/4 aggregate by volume. Samples having high dosage of micro-fillers and thus a higher binder volume achieved excellent values of both compressive (from 31 to 48 MPa in 28 days, and from 67 to 93 MPa in three years) and flexural strength (from 6.3 to 8.4 MPa in 28 days, and from 7.1 to 11.1 MPa in three years). Both samples with brick powder and concrete powder achieved the biggest strength values; however, due to better performance in durability parameters (capillary water absorption coefficient and density), sample prepared with glass powder can be identified as having the biggest potential for intended use.

Automatic image analysis process to appraise segregation resistance of self-consolidating concrete

The segregation of coarse aggregate in self-consolidating concrete (SCC) can result in some defects in the long-term properties of concrete. In this study, an image processing algorithm has been proposed and implemented, using standard coding languages, to assess segregation of the SCC mixtures. This algorithm has been designed to evaluate the distribution of coarse aggregate and the average thickness of the mortar band layer of SCC. Seven mixtures containing fly ash and silica fume as partial replacements for cement were analysed. Slump, J-ring flow and compressive strength of the samples were also measured. The results revealed that an increase in fly ash replacement resulted in a higher segregation index and a higher ratio of mortar band thickness. However, substitution of silica fume caused a lower segregation index and a lower ratio of mortar band thickness. The results demonstrate that there is a high degree of correlation between the segregation index and the mortar band thickness in all the mixtures.

Long-term properties of concrete containing limestone powder

Plain cement concrete (employed as reference) and three concretes containing limestone powder (replacement ratios of 10, 20, and 30%) were designed. The compressive strengths of the four concretes were close to each other by adjusting the water to binder ratios. The long-term (as long as 5 years) properties of hardened paste and concrete were determined under the condition of equal 28-day compressive strength of concrete. The results show that limestone powder can react with cement but its reaction degree is very low even at 5 years. The addition of limestone powder tends to increase the long-term connected porosity of concrete and the pore structure of hardened paste. The strength and resistance to chloride penetration of the concrete containing limestone powder increase much less than those of plain cement concrete at late ages. When the replacement ratio of limestone powder exceeds 10%, the resistance to carbonation of concrete decreases significantly, but the drying shrinkage of concrete is reduced.

Proposing new methods to appraise segregation resistance of self-consolidating concrete based on electrical resistivity

The static segregation of self-consolidating concrete (SCC) can lead to some problems in the long-term properties of concrete. While there are few methods to evaluate the risk of segregation, which some of them are not precise and applicable, proposing new methods can be beneficial. In this experiment, two methods based on electrical resistivity were used in order to appraise and compare different mixtures of self-consolidating concrete. In order to verify the attained results, column technique (ASTM C 1610) was also used.Seven mixtures containing fly ash and silica fume as partial replacements of cement were analyzed. Slump, J-ring flow and compressive strength of the samples were measured. The results revealed that increase in fly ash replacement resulted in higher segregation index (SI), higher periodic segregation index (PSI) and higher instant segregation index (ISI) at specific times. However, substitution of silica fume lead to lower SI, lower PSI and lower ISI at specific times. In overall, the results indicated that general trend of the mixtures is in good agreement with each other, and positive correlation between SI with PSI and ISI exist.

Long-term properties of concrete containing ground granulated blast furnace slag and steel slag

In this paper, the influence of six different mineral admixtures on the long-term properties of concrete within 1080 d is investigated; these admixtures include steel slag, ground granulated blast furnace slag (GGBS) and composite mineral admixtures with four different GGBS-to-steel slag ratios. The results show that steel slag and composite mineral admixtures with a high content of steel slag have many negative effects on the long-term properties of concrete, such as decreasing strength, increasing porosity and chloride penetrability, and decreasing carbonation and sulfate resistance. GGBS tends to improve the long-term properties of concrete. Concrete containing composite mineral admixture with a high content of GGBS can achieve similar long-term strength, porosity, chloride penetrability, and carbonation and sulfate resistance to Portland cement concrete. The influence of the composite mineral admixture composed of 80% GGBS and 20% steel slag on the long-term properties of concrete might be very close to that of GGBS. All the mineral admixtures tend to decrease the long-term drying shrinkage of concrete. The effect of composite mineral admixtures with higher GGBS content on the long-term drying shrinkage of concrete is more significant.

Activity Index of Steel Slag-GGBS Composite Mineral Admixture at Different W/B Ratios

The activity index of steel slag-GGBS composite mineral admixture with different steel slag contents at the W/B of 0.3, 0.4, and 0.5 was investigated. The results show that the activity index of the composite mineral admixture with higher GGBS content is larger, and this phenomenon is more obvious at later ages. At lower W/B, the gap of activity index of different composite mineral admixtures is smaller. The activity index of each composite mineral admixture is higher at lower W/B and at later age. The steel slag-GGBS composite mineral admixture is more suitable to be used in high strength concrete than in low strength concrete. As far as the long-term properties of concrete are concerned, the activity index of the composite mineral admixture at the late age should be adopted.

Shrinkage Deformation of Concrete Containing Recycled Coarse Aggregate

The long term properties of Concrete containing Recycled Coarse Aggregates (CRCA) were investigated. Initially, series of short term tests were carried out to determine the density, workability, absorption and compressive strength of concrete with and without locally available recycled aggregates from demolition wastes. The water cement ratio of 0.52 was adopted for all the mixes, while the coarse aggregate in concrete was replaced with 0%, 25%, 50% and 100% recycled coarse aggregates. The test results indicated that the replacement of normal coarse aggregates by recycled aggregates up to 25% had no significant effect on the compressive strength but higher levels of replacement reduced the compressive strength. A replacement level of 100% caused a reduction of about 27% in compressive strength. The shrinkage deformation characteristics of concrete made with 25% recycled coarse aggregate were compared with those of normal concrete. Eight 10cm x 10cm x 40cm concrete sealed and unsealed short columns made with and without RCA, were under investigation for 120 days. The results of the investigation showed that the basic shrinkage strains of normal concrete is about 1.07 times greater than that of CRCA (with Original Research Article Article British Journal of Applied Science & Technology, 4(12): 1791-1807, 2014 1792 25% RCA). The drying and total shrinkage strains of CRCA (with 25% RCA) are respectively 2.56 and 1.26 times greater than that of normal concrete. 25% RCA content in concrete was therefore considered for use in load bearing structural elements.

Utilization of Local Steelmaking Slag in Concrete

In this study, the use of locally produced electrical are furnace (EAF) steel slag in concrete manufacturing is investigated. The slag was used as coarse aggregate since it proved to be quite hard and did not contain any appreciable free chemical compounds of potentially adverse effects such as lime. For comparison, crushed wadi gravel was used in parallel to the slag. Mechanical properties as well as the drying shrinkage of both slag and gravel concrete were measured. The results showed compressive and flexural strengths for slag concrete to be similar to slightly higher than gravel concrete, splitting tensile strength and modulus of elasticity to be higher and drying shrinkage to be lower than that of gravel concrete. The results of this investigation are encouraging since they show that using slag as coarse aggregate in concrete has no negative effects on short term properties of hardened concrete. However, further investigation on the effect of steel slag on the long term properties of concrete is required before a recommendation can be given for using the steel slag as coarse aggregate in concrete.