Key Engineering Materials Vol. 668

Abstract: This paper aims the evaluation of water absorption and compressive strength of calcined clay lightweight aggregates produced using alkaline activators. The characterization of ceramic material was made by techniques of liquid and plasticity limits, particle size analysis and chemical analysis. The specimens made from these ceramic materials and alkali activators (potassium silicate, sodium silicate with NaOH (15M), phosphoric acid, sodium silicate, potassium hydroxide and sodium hydroxide) were burned at temperatures of 600 °C and 900 °C and they were characterized by evaluation of water absorption and compressive strength. Results of this research indicates that the burn temperature has influence on the final properties of calcined clay lightweight aggregates and, when this aggregates were made using some activators, as sodium silicate, they presented lower values of water absorption and higher values of compressive strength, for both burn temperature, which can generate significant energetic gain in the aggregates production process).

Abstract: Large amounts of ceramic sanitary-ware waste are generated in both the production process and construction and demolition practices. This waste contains amorphous phases that may react with the Portlandite that originates during Portland cement hydration or with an alkali solution, leading to a low CO₂-binding material. This study investigated the pozzolanic activity of ceramic sanitary-ware waste, together with its potential to form new binders by alkali activation. For this purpose, raw material was characterized by X-ray diffraction, X-ray fluorescence, particle size distribution, thermogravimetry (TGA) and scanning electron microscopy (SEM). Percentages of ceramic waste of 15 wt.% and 25 wt.%, to replace Portland cement, were used to assess the pozzolanic behavior of this material, and samples were cured at 20oC for different curing times. Alkali-activated samples, in which Ca (OH)₂ was used as a source of calcium, and NaOH and sodium silicate solutions were utilized as activators, were cured for 7 days at 65oC. The microstructural evolution of the developed binders was assessed in pastes by SEM and TGA analyses, and mortars were used to evaluate the compressive strength behavior. While some strength gain was observed due to pozzolanic activity, compressive strength values within the 14-36 MPa range were obtained in the alkali-activated mortars in accordance with the activator concentration and the percentage of Ca (OH)₂ addition.

Abstract: The aim of this study is to investigate the effects of phosphogypsum on the properties of both cement pastes and mortars. Normal Portland cement CEM Ι 32,5N, Limestone Blended cement CEM ΙΙ B-L32,5N, and Slag cement CEM ΙΙ A-S32,5N were used. These cements were partially substituted by 0,2,4,6,8,10,and 15% of phosphogypsum. The test program was divided to two stages. In the first stage, tests were conducted according to BSEN 196, namely setting times (initial and final), soundness, and compressive strength (at ages 7 and 28 days). In the second stage, X-ray diffraction (XRD), and scanning electron microscope (SEM) were conducted on selected mixes from first stage. The results show that the three types of cements with the various replacement percentages of phosphogypsum met the limit of initial setting time, as well as, provided soundness of 2 mm. Also, in terms of compressive strength, it was proven, that it is possible to partially replace the three tested types of cements by phosphogypsum by up to 8%and 15% with regard to cement/sand ratio of (1:3) and (1:2) respectively.

Abstract: The aim of this study is to investigate the effects of incorporating dune sand as fine aggregates replacement in self-compacting concrete. Twelve mixes were cast and tested for both fresh and hardened properties. The mixes were divided into 2 groups: Each group comprised six mixes. The constituent materials were as follows: Normal Portland cement CEM Ι 42,5N, dolomite as coarse aggregates of maximum size 10 mm, medium-sized sand, silica fume was 10% by weight of cement. Coarse: fine aggregates ratio was 1:1. Admixture which complies with ASTM C494 Types G and F was used in the 12 mixes (3.5% by weight of cement ).Dune sand replaced natural sand by zero %,10%,25%,50%, 75%,and 100% respectively .For , the first group (Group A), the cement content was 350 Kg/m³, while for the second group (Group B), the cement content was 400 Kg/m³.Tests carried out on fresh self-compacting concrete were slump flow,T_50cm ,V-funnel, V-funnel _t5min ,and GTM screen stability test . Tests conducted on hardened concrete were compressive strength at ages 7 and 28 days, flexural, and splitting tensile strengths were also conducted at age 28 days. The obtained results showed that the fresh properties satisfied the Egyptian Technical Specification limits. Regarding the hardened properties, both 28 days compressive and flexural strengths exhibited improvement till 50% replacement when compared to their respective control mixes.

Abstract: This study aims to investigate the properties of CDW recycled aggregates using silane-based water repellent agent in three different types of treatments: (a) immersion; (b) sprinkling; and (c) dripping; in order to improve the reduces quality of the material due to the high porosity. Wettability and water absorption were determined by apparent contact angle measurements, water absorption after 24h of saturation (standard method) and recording the variation of submerged mass during 24 hs. All treatment allowed reducing the water absorption and its kinetic. The contact angle measurements confirmed the effectiveness of the treatment: the surface resulted always hydrophobic. Comparing the treatments, immersion gave the best result in terms of absolute results and in terms of variability of measurements.

Abstract: Earthen masonry is generally brittle, weak and susceptible to water ingress damage. Several techniques of earthen masonry stabilization and reinforcement are available for improving their overall engineering properties. However, the inclusion of fiber into soils has a unique advantage. This is because friction between fibers and soil particles increases bonding between the particles. The present study attempts to investigate the resultant strength and ductility behavior when 0.5%, 1% and 2% randomly distributed human hair fibers are used to reinforce both cemented and un-cemented clayey-sand (50% sand and 50% bentonite) soils. The composite soils were tested under laboratory conditions and examined for compaction and unconfined compression strength (UCS) tests. The experimental results show that stress-strain behavior, failure, and strength characteristics of clayey-sand improved with inclusion of fibers. However, the effect of fiber reinforcement is more significant with stabilized clayey sand compared with the control soil mixture. Based on the compressive strength , the cement stabilization had better strength with bentonite clayey sand (50% sand and 50% bentonite) compared to the lime treatment. Addition of cement and lime affected dry density , optimum moisture content, and failure strain of the clayey-sand.

Abstract: In South America, especially in the Andean region, many communities are isolated and their development is limited due to the difficulties in communicating with urban areas, because the lack of adequate road infrastructure. Most of this problem is due to economic issues and lack of attention from governments. Moreover, the Guadua angustifolia Kunth (Guadua-a.) is a bamboo that grows in most of the Americas. This material has a resistance – weight ratio similar to structural steel also presenting additional benefits such as soil stabilization, flow regulation, and a high CO2 fixation rate to the ground. In addition the Guadua-a. growth cycle spans from 3 to 5 years. All of these makes the Guadua-a. in highly renewable material. This paper presents an alternative for the construction of Guadua-a. structural modules for pedestrian bridges, as a solution to the lack of infrastructure in village roads and even in suburban areas. In the proposed model, the bridge would be built by the community in a short time, taking advantage of existing Guadua-a. in the area, and establishing an industrialized cultivation of it, to enable them to have enough material for maintenance and replacement of sections as necessary. A numerical structural analysis was performed to determine the maximum possible span under load specifications from Colombian bridge building code. The results shows that a bridge up to 21m of span can be constructed using the module. The span can be increased drastically when the module is combined with wire-cable or an arc shaped configuration, however, the module was assessed to be used in straight truss bridges because this setting carries the largest loads on the elements. Real scale load tests were conducted on a full scale physical model of the module, the structural elements and the connection between the modules.

Abstract: In Colombia, as in other developing regions, social housing shortage related problems has led local authorities to propose low cost housing projects that allow its quickly and easy construction. Among the requirements of this type of construction are solicitations for vertical and lateral loads caused by wind or earthquake forces, as well as the sustainable use of natural resources Considering this, the use of Guadua angustifolia Kunth (Guadua a.) as a structural material has awaken a great interest, considering its renewability, high-speed growth, ecological benefits and because is easily obtainable all across the country. Due to the lack of additional information, structural joints in this type of materials, are usually pinned, assuming that there is no moment transmission between the different elements, however, some types of connections can partially restrict the rotation in the supports. Additionally, the degree of constrain that any support can provide to the column is a variable that has not been studied enough, despite being essential for modeling and structural design.In this work a connection between a column of Guadua a. and its foundation was studied. The influence of each component on the connection behavior under horizontal loads was assessed, testing seven different configurations. Monotonic and dynamic testing of connections as well as the characterization of the materials used in its construction were included in the experimental schedule. It was determined that the presence of mortar grouting together with the use of longitudinal bolts slightly increases the connection strength as drastically reduce its ductility. The use of transversal bolts is the best alternative to obtain a strong, stiff and ductile connection, especially when are combined with the use of hoops.

Abstract: The use of compressed earth blocks (CEBs) is widespread in the field of earth construction. They present better mechanical performance than adobe and the equipment for their production is simple. Laboratory testing of compressed earth blocks requires large amounts of material. There are variations of unconfined strength testing procedures such as testing halves of the blocks with layers of mortar between them or testing whole blocks in diverse directions. This complicates the interpretation of test results as the shape factor and mortar characteristics influence the results significantly. Static compaction test can be used to produce cylindrical samples representative of CEBs. The water content of soil used for the production of CEBs is often determined in standard Proctor test while experimental data indicate that the optimum moisture content for static and dynamic compaction is different. The present article addresses the behavior of four soil mixes with varying clay content compacted statically with a constant rate of strain. Static compaction curves were compared with those obtained in standard Proctor test. For all the soil mixes the static optimum moisture content was found to correspond to the start of consolidation. The compaction curve presented no wet side of optimum in contrast to Proctor test. The energy needed to achieve a desired density by static compaction was analyzed for soils with varying clay contents. Static compaction was found to be more efficient than dynamic for clayey soils. An increase in water content was observed to help achieving higher densities at low pressures, which can improve the performance of manual CEB presses.

Abstract: Concrete is the single most widely used material in the world and is only surpassed by water in terms of consumption. By 2013, 4 billion tonnes of Portland cement were produced worldwide, enough to produce about 32 billion tonnes of concrete, which represents more than 4.6 tonnes of concrete per person per year. The high water consumption and large amount of wastewater generated in the concrete industry has become a very important environmental issue. Due to the large global use of concrete, it is essential to correctly assess the environmental impacts of this material including impacts related to water consumption. Life cycle perspective is important because it allows identifying and reducing water related potential environmental impacts associated with products. In concrete life cycle assessment, these impacts are not considered mostly because of lack of data. There are several methodologies for water footprint assessment, as The Water Footprint Assessment Tool and the ISO 14046:2014 standard -that is based on life cycle assessment (ISO 14044)-, as well as sustainable reporting guidelines, which include water assessment for organizations. The aim of this paper is to evaluate existing water footprint methodologies based on life-cycle assessment, their concepts and difficulties, and link them to concrete industry. Out of at least eighteen existing water footprint methodologies, it was found that four of them are feasible for cement based materials industry, however there are differences between the definitions and criteria adopted by each methodology.