Effect of partial replacement of fine aggregate by internal curing materials on mechanical properties of concrete

Internal curing has long been utilized to decrease self-shrinkage and consequently the increased danger of concrete cracking prematurely. The measured mechanical characteristics of concrete were studied in five mixes, both with and without internal curing. Two of these mixtures have a 10% replacement rate, with one using ceramic and the other Attapulgite, while the other two have a 20% replacement, with one using ceramic and the other using Attapulgite, and the fifth is a reference mixture with no replacement for comparative reasons. With an increase of 27.93%, the ceramic combination with a 20% replacement rate is judged to have the highest compressive resistance, followed by the Attapulgite mixture with a 20% replacement rate with an increase of 34.2%. The results showed that the ceramic and Attapulgite internal curing purposes were highly effective, especially with a 20% replacement. The use of crushed ceramics and attapulgite as internal curing materials improves the characteristics of concrete.

The Effect of Adding Fibers on Dry Shrinkage of Geopolymer Concrete

Despite their drastically different chemical ingredients and interactions, geopolymer concrete exhibits many of the same features as ordinary concrete. Among these properties is drying shrinkage. As in normal concrete, dry shrinkage in geopolymer concrete may cause cracking if the geopolymer concrete is bound, which affects the integrity of the structure in the future. It's important to measure drying shrinkage as soon as possible because it's the cause of early age cracking, which happens when the concrete isn't very strong. The purpose of this study is to determine how to reduce the dry shrinkage value of geopolymer concrete by using different types of fibers. Three types of fibers were used to determine their effect on the dry shrinkage of geopolymer concrete when compared with a reference mixture without the fibers. Metakaolin was used as a binder for the concrete geopolymer. As for the fibers, steel, carbon and polypropylene fibers were used in proportions of (0, 0.5, and 1%). The results showed an improvement in dryness shrinkage when adding fibers in general, with a difference in values between the different types of fibers. Steel fibers had the lowest amount of dry shrinkage. The temperature had a direct influence on the decrease in the extent of the shrinking, since the samples handled at higher temperatures had less dryness to begin with. Doi: 10.28991/cej-2021-03091780 Full Text: PDF

Use of Ash after Denitrification as an Additive to Concrete Based on Alcali-Activated Slag

This paper deals with the possibility of using fly ash after denitrification by the SNCR method a partial replacement in alkali-activated concrete based on blast furnace granulated slag. Previous research has verified the use of fly ash after denitrification in alkali-activated materials based on blast furnace granulated slag, and so far no negative effects on the properties of these mixtures have been found. The tests were performed on cement test specimens. As part of the preparation of concrete mixtures, two recipes were prepared. The first reference mixture contained only blast furnace granulated slag activated by sodium water glass with silicate modulus of 2. The second recipe was modified by replacing of 30% slag by fly ash after denitrification by SNCR method. Within the strength characteristics, the reference mixture always achieved better results. Very slow increases in strength were recorded for the mixture with 30% slag replacement by fly ash, when the compressive strength after 7 days of maturation was only 4.5 MPa.

Possibilities of Using Pumice Concrete as Thermal Insulation Lining of Industrial Chimneys

This paper deals with the possibility of using pumice concrete as thermal insulation lining of industrial chimneys. Two formulas were prepared, the first from sulphate resistant cement and the second as a reference mixture from Cem I 42.5R. The thermal insulating properties of the prepared recipes will be evaluated as well as the resistance to the action of sulphates in 5 % sodium sulphate solution. No significant decrease in strength was observed when samples were stored in 5% sodium sulfate solution for 60 days. Only the reference series reported a significant unexpected decrease in strength.

A Preliminary Laboratory Evaluation on the Use of Shredded Cigarette Filters as Stabilizing Fibers for Stone Mastic Asphalts

Cigarette butts can be considered as one of the most common contemporary sources of waste, considering the large consumption of cigarettes all over the world. Despite the fact that different solutions have been developed and tested in the recent years aiming to recycle them, cigarette butts are currently landfilled and incinerated. Following the circular economy principles, the experimental application proposed in this paper is an exploratory investigation on the use of shredded cigarette filters as sustainable alternative to the addition of fibers into Stone Mastic Asphalts (SMAs). This represents the preliminary step for a wider research project, aiming to find a possible recycling solution for cigarette butts as fibers in bituminous materials. The use of fibers is a common and well-established solution for the production of high bitumen content mixtures. The fibers have a double function: acting, generally, as a stabilizing agent and, where possible, improving the mechanical performance of the bituminous mixtures. In the present research, two different SMAs were produced and tested aiming to analyze the effects given by the addition of the shredded cigarette filters. The first asphalt concrete, produced with traditional cellulose fibers was taken as a reference mixture, while the experimental mixture was produced with the shredded cigarette filters. The data highlight interesting and promising results for future development, making the use of waste cigarette filters a potential eco-friendly alternative to common cellulose fibers for SMAs.

Durability of concrete exposed to sulfuric acid attack

This thesis investigates the effects of aggressive sulfuric acid attack on the concrete mixtures prepared with metakaolin (MK) and limestone filler (LF) at various replacement levels. In addition, rapid chloride permeability (RCPT), water sorptivity, water porosity and rapid freezing and thawing tests were also performed on the concrete samples. Three sulphuric acid solutions with concentrations of 3%, 5% and 7% were used for examining the resistance of concrete specimens for a total exposure period of eight weeks. The performance of the degraded specimens was evaluated by measuring the weight loss, change in strength and visual assessment. The results of the weight loss and visual assessment reveal that the increase in the amount of MK would enhance the performance of concrete, while inclusion of LF into MK concretes has shown positive results in terms of resistance against sulphuric acid attack. The mixtures with ternary binders of OPC, MK and LF experienced the lowest strength loss after exposure to high concentrations of sulphuric acid. Measuring the change of weight was found to be a better way to evaluate the resistance of concrete specimens immersed in sulfuric acid solutions as the results of the load bearing capacity can be affected by several parameters such as the variable geometry of degraded specimens. The rate of the water absorption of concrete with MK and LF was lower than the reference mixture with only Portland cement. The RCPT results also showed that the reference mixture had considerably higher permeability than other concrete mixtures. The results of the water porosity on degraded samples indicate that the inner parts of the concrete (not in contact with sulfuric acid) have remained sound and maintained their original pore structure after different exposure periods.

Durability of concrete exposed to sulfuric acid attack

This thesis investigates the effects of aggressive sulfuric acid attack on the concrete mixtures prepared with metakaolin (MK) and limestone filler (LF) at various replacement levels. In addition, rapid chloride permeability (RCPT), water sorptivity, water porosity and rapid freezing and thawing tests were also performed on the concrete samples. Three sulphuric acid solutions with concentrations of 3%, 5% and 7% were used for examining the resistance of concrete specimens for a total exposure period of eight weeks. The performance of the degraded specimens was evaluated by measuring the weight loss, change in strength and visual assessment. The results of the weight loss and visual assessment reveal that the increase in the amount of MK would enhance the performance of concrete, while inclusion of LF into MK concretes has shown positive results in terms of resistance against sulphuric acid attack. The mixtures with ternary binders of OPC, MK and LF experienced the lowest strength loss after exposure to high concentrations of sulphuric acid. Measuring the change of weight was found to be a better way to evaluate the resistance of concrete specimens immersed in sulfuric acid solutions as the results of the load bearing capacity can be affected by several parameters such as the variable geometry of degraded specimens. The rate of the water absorption of concrete with MK and LF was lower than the reference mixture with only Portland cement. The RCPT results also showed that the reference mixture had considerably higher permeability than other concrete mixtures. The results of the water porosity on degraded samples indicate that the inner parts of the concrete (not in contact with sulfuric acid) have remained sound and maintained their original pore structure after different exposure periods.

Analysis of the influence of partial replacement of mineral aggregate by basaltic rock dust on the production of industrialized adhesive mortar

The production of adhesive mortar uses large proportions of sand, causing undesirable environmental impact as this is a finite resource. In recent years, the insertion of civil construction waste in cement matrixes has intensified with the objective of replacing sand in the mortar manufacturing process. Therefore, in this study, the proportions of 5%, 10%, 15% substitution of the mineral aggregate by basalt dust waste in the production of industrialized adhesive mortar were adopted. The reference mixture of 1:3 (cement: sand) was adopted and the water/dry material ratio was set at 0.20. The adhesive mortars produced in the tests to determine the consistency index, water retention, mass density, open time, tensile strength and water absorption by capillarity were analyzed. The results were satisfactory, demonstrating that it is feasible to use the waste as a substitute for sand in the production of industrialized adhesive mortars.

Effect of Admixtures on Durability Characteristics of Fly Ash Alkali-activated Material

This paper deals with the possibility of partial replacement of blast furnace slag with fly ash and fly ash after denitrification by SNCR method in alkali-activated materials based on granulated blast furnace slag. The aim of this paper is to verify the effect of fly ash on properties of alkali-activated materials based on blast furnace granulated slag. Frost resistance and resistance to aggressive environments, represented by demineralized water were tested. The reference mixture was based on blast furnace granulated slag activated by sodium water glass with silicate modulus of 2. Mixtures with an ash content of 10, 20, and 30% were then compared with the reference mixture. The influence of the denitrification process on fly ash and its use in mixed alkali activated materials was also compared. As a part of the experiment, alkali-activated pastes were also prepared. Infrared spectroscopy with Furier transformation was subsequently determined on these pastes. The reference mixture achieved the highest compressive strength in the experiment and the strength decreased with increasing amount of fly ash. In terms of flexural strength, the highest values were reached for mixtures with 10% slag replacement by fly ash. In the case of frost resistance, the significant increase of flexural strength, which was 50% for the reference mixture, is particularly interesting. For compressive strength, the frost resistance coefficient ranged from 0.95 to 1.00. In the case of resistance to aggressive environments, no differences were observed in the compressive strength, on the other hand, flexural strength decrease of up to 20% was detected for 10 and 20 percent replacement of slag with fly ash that did not undergo denitrification. Monitored properties did not show any negative effect of the denitrification process on fly ash properties. Infrared spectroscopy identified the main hydration product in the region of 945 cm-1which is a C-(A)-S-H gel and in combined mixtures with fly ash also N-A-S-H gel. Doi: 10.28991/esj-2020-01247 Full Text: PDF