Search Results (10)

Practical use of calcium sulfoaluminate cements (CSAs) is dependent on their compatibility with admixtures. The following paper presents research into the effects of three different superplasticizers (SPs) (polycarboxylate ethers, modified polycarboxylates, and polynaphthalene sulfonate), and the effect of a w/c ratio in a range of 0.45–0.35 in mortars containing superplasticizer on the chosen mortar properties. The conducted tests related to consistency, initial setting time, hydration heat, flexural and compressive strength, early shrinkage (first 20 h), and drying shrinkage. The results indicate that the superplasticizer type has significant effect on the properties of CSA mortars. All superplasticizers prolonged the initial setting and induction phase of hydration in relation to CSA mortar which did not contain superplasticizer by up to 109%; however, their effect on compressive and flexural strength, drying shrinkage, and early shrinkage was dependent on the type of superplasticizer involved. Polycarboxylate ether SP provided the best results for mortar properties, as it did not affect compressive strength significantly, but reduced plastic shrinkage. Polynapthalene-based SP decreased strength and increased shrinkage more than other superplasticizers, making it the least compatible. Decreasing the w/c ratio for mortar containing superplasticizer allowed us to mitigate some of the issues, as mortars with SP1 in a low w/c ratio exhibited higher compressive and flexural strength by, respectively, 41% and 80% in the case of a w/c ratio of 0.35, and lower shrinkage. Full article

The incorporation of circulating fluidized bed (CFB) fly ash into self-leveling cement-based (SLC) paste production presents significant environmental advantages. However, its addition deteriorates the fresh properties of the paste, posing challenges for practical implementation. This research examined the fresh properties of SLC paste blended with CFB fly ash, emphasizing fluidity, rheological characteristics, and bleeding rate. To enhance flowability, polycarboxylate superplasticizer (PCE) was incorporated, with particular emphasis on its interaction with CFB fly ash. The findings reveal that adding CFB fly ash to cement-based paste significantly decreased fluidity while increasing yield stress and plastic viscosity. Incorporating 20 wt.% CFB fly ash reduced paste fluidity by 51.4%, while plastic viscosity and yield stress increased by factors of 2.3 and 73, respectively. While PCE enhanced the fluidity of the blended paste, its water-reducing efficiency diminished, and the bleeding rate of the paste increased with higher CFB fly ash dosage. The water-reducing capability of PCE in the CFB fly ash-blended cement paste with 20 wt.% CFB fly ash decreased by 40.0%, and the bleeding rate of the paste increased from 0.6% to 6.7%. This effect was primarily attributed to the poor compatibility between PCE and CFB fly ash. The decline in PCE efficiency with higher CFB fly ash content, along with its lower adsorption capacity on CFB fly ash compared to cement particles, further confirmed this incompatibility. Full article

The incorporation of polycarboxylate ether superplasticizer (PCE)-type polymers and silica fume (SF) in high-performance concretes (HPC) leads to remarkable rheological and mechanical improvements. In the fresh state, PCEs are adsorbed on cement particles and dispersants, promoting the workability of the concrete. Silica fume enables very well-compacted concrete to be obtained, which is characterized by high mechanical parameters in its hardened state. Some PCEs are incompatible with silica fume, which can result in slump loss and poor rheological behavior. The main objective of this research is to study the influence of three types of PCEs, which all have different molecular architectures, on the rheological and mechanical behavior of high-performance concretes containing 10% SF as a partial replacement of cement. The results show that the carboxylic density of PCE has an influence on its compatibility with SF. Full article

The paper deals with the effectiveness of various types of polymers (naphthalene formaldehyde, polycarboxylate, and lignosulfonate) as superplasticizers of concrete mixtures based on low-clinker slag Portland cement. Using the mathematical planning experimental method and statistical models of water demand of concrete mixtures with polymer superplasticizers, as well as concrete strength at different ages and under different curing conditions (normal curing and after steaming) were obtained. According to the models, the superplasticizer’s water-reducing effect and relative change in concrete strength were obtained. The proposed criterion for evaluating the effectiveness and compatibility of superplasticizers with cement takes into account the water-reducing effect of the superplasticizer and the corresponding relative change in concrete strength. The results demonstrate that the use of the investigated superplasticizer types and low-clinker slag Portland cement allows for achieving a significant increase in concrete strength. The effective contents of various polymer types, which allow the achieving of concrete strengths from 50 MPa to 80 Mpa, has been found. Full article

Poor workability is a common feature of calcium sulfoaluminate (CSA) cement paste. Multiple chemical admixtures, such as set retarders and dispersants, are frequently employed to improve the workability and delay the setting of CSA cement paste. A quantitative assessment of the compatibility, efficiency, and the effects of the admixtures on cement paste workability is critical for the design of an appropriate paste formulation and admixture proportioning. Very limited studies are available on the quantitative rheology-based method for evaluating the workability of calcium sulfoaluminate cement pastes. This study presents a novel and robust time-dependent rheological method for quantifying the workability of CSA cement pastes modified with the incorporation of citric acid as a set retarder and a polycarboxylate ether (PCE)-based superplasticizer as a dispersant. The yield stress is measured as a function of time, and the resulting curve is applied to quantify three specific workability parameters: (i) the rate at which the paste loses flowability, (ii) the time limit for paste placement or pumping, marking the onset of acceleration to initial setting, and (iii) the rate at which the paste accelerates to final setting. The results of the tested CSA systems show that the rate of the loss of flowability and the rate of hardening decrease monotonously, while the time limit for casting decreases linearly with the increase in citric acid concentration. The dosage rate of PCE has a relatively small effect on the quantified workability parameters, partly due to the competitive adsorption of citrate ions. The method demonstrated here can characterize the interaction or co-influence of multiple admixtures on early-age properties of the cement paste, thus providing a quantitative rheological protocol for determining the workability and a novel approach to material selection and mixture design. Full article

The influence of grinding aids (pure triethanolamine and ethylene glycol) on the properties of cements, their compatibility with an acrylate-based superplasticizer and the rheological parameters of mortars were investigated. The presence of surfactants influences the standard properties of cements and the effectiveness of the superplasticizer. The results of the heat of hydration and setting time measurements indicate a delay in the hydration process and an increase in the induction period duration of the surfactant-doped pastes, in relation to the reference sample without grinding aids. Triethanolamine increases early-age compressive strength; the effect was observed for both standard and superplasticizer-containing mortars. The presence of grinding aids decreases the slump flow of mortars and increases rheological parameters such as yield stress (τ₀) and viscosity (η). Full article

Due to their exceptional electrical properties, carbon nanotubes (CNTs) can be applied as conductive fillers to develop self-sensing cement-based matrices. In order to obtain an adequate self-sensing response, CNTs must be evenly dispersed through the cement matrix in a volume sufficient enough to create an electric percolation network. This is challenged by the difficulty of dispersing CNTs; therefore, there is a demand for an efficient dispersing agent that can be filled by superplasticiezers, which are products of known compatibility with cement and high availability. This research explores the use of four commercial superplasticizers available in Brazil, both naphthalene and ether polycarboxylate-based, as dispersing agents for CNTs in water. Ultrasonic energy was applied to aqueous solutions containing CNTs and superplasticizers. UV–Vis spectroscopy and ξ-potential measurements were used to investigate which superplasticizer was more effective to disperse the CNTs. Cement pastes were produced with the CNT dispersions and their electrical resistivity was measured. It was found that only superplasticizers without aliphatic groups in their structure were capable of dispersing CNTs in water. It was concluded that second-generation naphthalene-based superplasticizers were more efficient dispersing agents for CNTs than third-generation ether polycarboxylate-based ones for self-sensing applications. Full article

The use of construction and demolition waste (CDW) to prepare recycled admixtures is of great significance for the complete resource reutilization of CDW. In this paper, different kinds of CDW were prepared into recycled powder (RP) with a specific particle size (0–45 µm or 0–75 µm). The fineness, water requirement ratio (WRR), fluidity, loss on ignition (LOI), strength activity index (SAI) and compatibility of cement and superplasticizer (CCS) were examined. The above test results were analyzed by advanced analysis tools, such as laser particle size analysis, XRD, XRF, DSC-TGA, SEM, and BET. The properties of different types of RPs varied greatly, which was closely related to the microstructure, particle morphology and chemical composition of the RP. The experimental results showed that all kinds of RPs after grinding had a high fineness and good particle size distribution, and the mineral composition was dominated by SiO₂ with the content exceeding 50%. The WRR of various RPs was between 105% and 112%, and the SAI was between 68% and 78%, but the LOI varied greatly. Different types of RPs had a negative impact on the CCS, but the compatibility of cement and naphthalene-based superplasticizer was less affected. The content of recycled brick powder (RBP) in a hybrid recycled powder (HRP) was an important factor. When the content of RBP in HRP exceeded 50%, the HRP could meet the basic performance requirements of fly ash. Full article

This paper deals with the behavior of concrete’s self-compatibility in a fresh state and its compressive and flexural strength in a hardened state with the addition of polyolefin macro fibers. Four different amounts (3 kg/m³, 4.5 kg/m³, 6 kg/m³, and 9 kg/m³) of polyolefin macro fibers were mixed into the concrete mixture to observe the differences in workability and strength properties between the concrete specimens. As a partial replacement of cement, class C type of fly ash was added to make up 25% of the total cement mass. The water-binder ratio (W/B) of the concrete mix was 0.36. Superplasticizer was added to the concrete mixture to achieve self-compacting properties. The slump test was carried out in the fresh state for determining the flowability. On the 7th and 28th days of the curing process, compression strength tests were performed, and on the 28th day, flexural strength tests and crack mouth opening displacement (CMOD) analyses were carried out to determine the strength properties and post-cracking behavior of the concrete samples. Bending strength and post-cracking behavior of the samples were improved by the addition of fibers. The fiber concentration in the concrete mixture greatly influenced the slump flow and self-compaction properties. Full article

The paper deals with the effectiveness of an innovative phosphonate-based superplasticizer (PNH) for ready mixed concrete. Concrete specimens were manufactured by considering a constant initial workability, equal to 220 mm slump at the end of the mixing procedure. Workability was measured at 0, 30, and 60 min to evaluate the workability retention performances of the innovative superplasticizer. Compressive tests at 1, 7, and 28 days were carried out to evaluate the influence of the phosphonate-based superplasticizer on concrete setting and hardening. The concrete mixes were designed by considering 13 different cements to assess the superplasticizer-cement compatibility. The PNH-based admixture showed a better performance in terms of water reduction and workability retention with respect to napthalenesulphonate based admixtures (NSF); however, a higher dosage of PNH with respect to polycarboxylate ethers (PCEs) was needed to get the same initial fluidity. Full article