Engineering properties of sustainable green concrete incorporating eco-friendly aggregate of crumb rubber: A review

Evaluation of fracture processes under shear with the use of DIC technique in fly ash concrete and accurate measurement of crack path lengths with the use of a new crack tip tracking method

Validation of the favorable quantity of fly ash in concrete and analysis of crack propagation and its length – Using the crack tip tracking (CTT) method – In the fracture toughness examinations under Mode II, through digital image correlation

This paper presents the results of the fracture toughness of concretes containing two mineral additives. During the tests, the method of loading the specimens according to Mode I fracture was used. The research included an evaluation of mechanical parameters of concrete containing noncondensed silica fume (SF) in an amount of 10% and siliceous fly ash (FA) in the following amounts: 0%, 10% and 20%. The experiments were carried out on mature specimens, i.e., after 28 days of curing and specimens at an early age, i.e., after 3 and 7 days of curing. In the course of experiments, the effect of adding SF to the value of the critical stress intensity factor—KIcS in FA concretes in different periods of curing were evaluated. In addition, the basic strength parameters of concrete composites, i.e., compressive strength—fcm and splitting tensile strength—fctm, were measured. A novelty in the presented research is the evaluation of the fracture toughness of concretes with two mineral additives, assessed at an early age. During the tests, the structures of all composites and the nature of macroscopic crack propagation were also assessed. A modern and useful digital image correlation (DIC) technique was used to assess macroscopic cracks. Based on the conducted research, it was found the application of SF to FA concretes contributes to a significant increase in the fracture toughness of these materials at an early age. Moreover, on the basis of the obtained test results, it was found that the values of the critical stress intensity factor of analyzed concretes were convergent qualitatively with their strength parameters. It also has been demonstrated that in the first 28 days of concrete curing, the preferred solution is to replace cement with SF in the amount of 10% or to use a cement binder substitution with a combination of additives in proportions 10% SF + 10% FA. On the other hand, the composition of mineral additives in proportions 10% SF + 20% FA has a negative effect on the fracture mechanics parameters of concretes at an early age. Based on the analysis of the results of microstructural tests and the evaluation of the propagation of macroscopic cracks, it was established that along with the substitution of the cement binder with the combination of mineral additives, the composition of the cement matrix in these composites changes, which implies a different, i.e., quasi-plastic, behavior in the process of damage and destruction of the material.

Studies of Fracture Toughness in Concretes Containing Fly Ash and Silica Fume in the First 28 Days of Curing.

Polyvinyl alcohol (PVA) fiber-reinforced geopolymer mortar is an eco-friendly construction material with excellent mechanical properties and durability. Visual observation, mass loss measurement, cubic and prism compressive tests , flexural tests, thermogravimetric and differential thermal analysis , scanning electron microscopy, and bubble parameter tests were conducted to evaluate the effect of PVA fiber and exposure temperature on the behavior of PVA fiber-reinforced geopolymer mortar after exposure to high temperatures. The PVA fiber contents were selected as 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, and 1.2%, and the target temperatures were 25 °C, 200 °C, 400 °C, 600 °C and 800 °C. The results indicate that significant mass loss of the geopolymer mortar could be observed when the exposure temperature increased from 25 °C to 250 °C, whereas slight mass loss occurred from 250 °C to 700 °C, and no mass loss was detected from 700 °C to 800 °C. As the temperature increased, the geopolymer mortar gradually densified, while the geopolymer mortar continuously developed more cracks and pores. The compressive and flexural strengths of the geopolymer mortar improved as the temperature increased from 25 °C to 200 °C, but it decreased significantly as the temperature further increased to 800 °C. In addition, on exposure to 200 °C, the presence of PVA fibers significantly improved the cubic and prism compressive strengths and flexural strength by 50.5%, 29.4%, and 66.3%, respectively, compared with the geopolymer mortar without fibers. As the temperature increased above 200 °C, although the PVA fiber decomposed, the defects left by the melt fibers slightly influenced the strength of the geopolymer mortar. 

High-temperature behavior of polyvinyl alcohol fiber-reinforced metakaolin/fly ash-based geopolymer mortar

Strengthening the very early-age structure of cementitious composites with coal fly ash via incorporating a novel nanoadmixture based on C-S-H phase activators

Modification of a cement matrix using additives and admixtures has been a common practice for many years. The use of some mineral additives as substitutes for the cement, e.g., the siliceous fly ashes (FAs), has a positive effect on reducing the energy used in cement production. On the other hand, such activities may have negative effects due to the lowering of strength parameters of composites in early stages of curing. In order to solve this problem, over the last few years, thanks to the patented "seedings" technology, a branch of industry connected with the production of admixtures that accelerate the binding process has developed significantly. Therefore, the paper presents the results of research aimed at analyzing the parameters of FA cement matrix with the nanoadmixture containing the nanometric C-S-H seeds (nanoadmixture (NA)). By using the modern NA, an attempt was made to neutralize the negative influence of the used industrial waste on the structure of the cement matrix in the early stages of its curing. The paper presents the results of strength tests for the FA cement pastes modified by NA in seven test periods, i.e., after 8, 12, 24 and 72 h, and 7, 14 and 28 days. Additionally, hydration heat tests were carried out on the analyzed material in the first 24 hours of curing.

https://www.mdpi.com/1996-1073/13/24/6734/pdf

Improvement of Strength Parameters of Cement Matrix with the Addition of Siliceous Fly Ash by Using Nanometric C-S-H Seeds

Siliceous fly ash (FA) is the main additive to currently produced concretes. The utilization of this industrial waste carries an evident pro-ecological factor. In addition, such actions have a positive effect on the structure and mechanical parameters of mature concrete. Unfortunately, the problem of using FA as a Portland cement replacement is that it significantly reduces the performance of concretes in the early stages of their curing. This limits the possibility of using this type of concrete, e.g., in prefabrication, where it is required to obtain high-strength composites after short periods of curing. In order to minimize these negative effects, this research was undertaken to increase the early strength of concretes with FA through the application of a specifically formulated chemical nano-admixture (NA) in the form of seeds of the C-S-H phase. The NA was used to accelerate the strength growth in concretes. Therefore, this paper presents results of tests of modified concretes both with the addition of FA and with innovative NA. The analyses were carried out based on the results of the macroscopic and microstructural tests in five time periods, i.e., after 4, 8, 12, 24 and 72 h. The results of tests carried out with the use of NA clearly indicate the possibility of using FA in a wide range of management areas in sustainable concrete prefabrication.

Application of the C-S-H Phase Nucleating Agents to Improve the Performance of Sustainable Concrete Composites Containing Fly Ash for Use in the Precast Concrete Industry.

The use of fly ash in cement composites adversely affects its mechanical properties during the first days of mixture curing. Modern technology, in the form of an admixture containing the hydrated calcium silicates, allows to accelerate the hardening and binding process of concrete. In this paper, studies on the influence of the admixture on properties of concretes with the ordinary Portland cements (OPC) containing the addition of siliceous fly ash (FA) have been carried out. As part of the experimental research, the authors conducted a series of studies for cement pastes modified with the addition of FA and the CSH nano-admixture (NA). In order to compare the mixtures, the following tests of cement pastes were carried out: the compressive and flexural strength, heat of hydration, SEM and rheological shrinkage. The mechanical parameters were tested after 4, 8, 12 and 24 h. The hydration heat test and microstructure analysis were carried out during the first 24 h of the concrete curing. All tests were carried out on the standard samples. On the basis of the heat of hydration test, much higher hydration heat was found in mixtures modified with the NA. During the shrinkage test, a positive effect of the NA was observed-the shrinkage during the first 28 days of mixture curing was lower than in the reference samples. The application of the CSH nano-admixture to cement pastes with the addition of FA has brought positive effects. Apart from a significant increase in strength in the first 24 h of mixture curing, a reduction in the rheological shrinkage was observed. The admixture can be successfully used in the ash concretes, in which a higher early strength is required.

https://www.mdpi.com/1996-1944/14/13/3640/pdf

Rheology of Cement Pastes with Siliceous Fly Ash and the CSH Nano-Admixture.

In the paper, the authors present the results of tests concerning traditional cement mortars with the addition of silica fly ash and the C-S-H nano-admixture. The use of fly ash results in improved plasticity of the mixture. The use of the C-S-H nano-admixture has a positive effect on shortening the setting time and a rapid increase in the strength of mixtures without losing their subsequent properties, which is presented in the research described in the paper. On this basis, the impact of fly ash and the nano-admixture on the selected parameters of the cement paste in the early maturation periods was determined – after 4, 8, 12, 24, 72h and also 7 and 28 days. The following tests were carried out on previously prepared samples: the compressive strength test on a hydraulic press, the test of setting time and the test of cement matrix shrinkage.

/pdf/modification-of-early-strength-parameters-of-concrete-by-the-4fkcnjcup8.pdf

Bartosz Szostak

Papers

Strengthening the very early-age structure of cementitious composites with coal fly ash via incorporating a novel nanoadmixture based on C-S-H phase activators

Improvement of Strength Parameters of Cement Matrix with the Addition of Siliceous Fly Ash by Using Nanometric C-S-H Seeds

Application of the C-S-H Phase Nucleating Agents to Improve the Performance of Sustainable Concrete Composites Containing Fly Ash for Use in the Precast Concrete Industry.

Rheology of Cement Pastes with Siliceous Fly Ash and the CSH Nano-Admixture.

Modification of early strength parameters of concrete by the addition of fly ash and admixture of nano C-S-H for application in 3D printing