This experimental study focuses on the assessment of mineral additives and their incorporation into cement composites (CC). The assessment was based on a holistic approach to the performance of the durability properties of CC. Environmental suitability was also taken into consideration. In the experiments, cement pastes with w/c ratios of 0.3, 0.4, and 0.5, respectively, were prepared. Natural zeolite (NZ) and densified silica fume (SF) at doses of 7.5 and 15.0 wt.% of cement were used as the investigated (replacement) materials. Their effects (including development over time) on density, strength (flexural and compressive), porosity by water absorption, permeability by rapid chloride penetration (RCP) test, phase content by thermal analysis, and hydration progression, were observed. The results were then used to propose an evaluation approach. Natural zeolite was used for its known pozzolanic activity and classification as a supplementary cementitious material (SCM). In contrast SF acted as a filler in cement pastes, and thus did not have a direct positive effect on durability. The concept of comprehensive analysis for unknown additive classification is proposed to expressly differentiate between SCM, inert, and improving mineral additive. This concept could be applied to the assessment of mineral additives with regards to the durability and suitability of cement composites.
This experimental study is focused on the aggregate gradation impact on the properties of fresh and hardened concrete. For the experiment, 9 mix design were prepared with the constant content of cement, effective water, plasticizer and aggregate. The variable factor is represented by different proportions of 4 fraction (0/0.7, 0/4, 4/8, 8/16). Consistency by slump and flow table in time, compressive strength, water absorption and density were measured. Some significant differences were observed. Consistency by the slump test varied from 0 to 170 mm after 5 minutes and from 0 to 50 mm after 30 minutes of concrete mixing. Consistency by flow table varied from 340 to 530 mm after 5 minutes and 320 to 460 mm after 30 minutes. Standard compressive strength varied from 50.8 to 61.6 MPa. Water absorption varied between 4.7 and 5.9 mass % and density from 2380 to 2440 kg.m−3.
Article contains experiment investigating influence of partial cement replacement by zeolite on consistency of fresh concrete, early compressive strength development and temperature development in early stages of curing. Four concrete mixture compositions were tested – containing zeolite in 0%, 5%, 10% and 15% of binder weight. Consistency was tested by flow table test in 5 minutes and 30 minutes after mixing of fresh concrete. Compressive strength and temperature gain were tested after 12, 16, 20 and 24 hours of curing. Results showed significant influence of zeolite on consistency of fresh concrete while compressive strength results were still in the acceptable range.
This article deals with the use of photovoltaic panels at the end of their life cycle in cement composites. Attention is focused on the properties of cement composite after 100% replacement of natural aggregate with recycled glass from photovoltaic panels. This goal of replacing natural filler sources with recycled glass is based on the updated policy of the Czech Republic concerning secondary raw materials for the period of 2019–2022, which aims to increase the self-sufficiency of the Czech Republic in raw materials by replacing primary sources with secondary raw materials. The policy also promotes the use of secondary raw materials as a tool to reduce the material and energy demands of industrial production and supports the innovations and development of a circular economy within business. The research has shown that it is possible to prepare cement composite based on recycled glass from solar panels, with compressive and flexural strength after 28 days exceeding 40 MPa and 4 MPa. Furthermore, a possible modification of the cement composite with different pigments has been confirmed, without disrupting the contact zone.
The article deals with the topic of a crystallizing waterproof admixture using in concrete. This type of admixture is designated for making a hardened concrete more durable by minimizing its permeability. Considering that concretes of higher strength classes meet the requirements for durability parameters in most cases, in this experiment 3 low-durability (in terms of high w/c ratio) concrete (Dmax8) batches were mixed. From each of mixture, 2 sets of samples (with and without the admixture) were prepared for depth of penetration of water under pressure test, strength test and water absorption test after 28 days of curing. Likewise, samples for microscopic visual assessment of crack-filling process were produced. Cracks onto these samples were intentionally introduced after their curing in time of 7 days and subsequently were further cured under water and regularly observed. According to the results, tested admixture acted more counter-productive than helpfully.
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