Journal of Building Materials and Structures

Conception of eco-friendly cement based on natural pozzolan to improve rheological behavior of concrete

2020-10-19T21:51:27+00:00

The pozzolan of Beni- Saf region (North-West Algeria) is a natural material of volcanic origin with an ability to react with lime in the presence of water and to form compounds with binding properties. Therefore, its use in the production of new cementitious materials will protect the environment. It will therefore be interesting to exploit this source as a partial cement substitution. In this work, a rheometric investigation was carried out to assess the performance of the natural pozzolan substituted to cement at variable rates ranging from 5%, 10%, 15% to 20% in order to obtain an ecological concrete. As the rheological behavior of concrete depends on the behavior of the cement paste, the effect of pozzolan on the latter was analyzed using static flow tests and dynamic creep and oscillation tests. The results of the rheometric tests have shown that in flow, the pozzolan improves the fluidity and in oscillation mode, it generates a viscous behavior of the cementitious pastes compared to elastic behavior of the control paste. Furthermore, the transient study (creep / recovery) made it possible to highlight the liquid viscoelastic character of the cement pastes. With 10% of pozzolan, the rheological behavior of the paste is viscous liquid which seems to be the best. The use of pozzolan as cement substitution has significant economic, environmental and technical advantages, namely the development of natural pozzolan, reduction of CO₂ emissions during the manufacture of cement as well as energy reduction and finally improvement of the properties of fresh concrete.

Analysis of Aqueducts Subjected to Hydrostatic and Dynamic Loads Using 3D - Solid Modeling

2020-10-19T21:52:19+00:00

In many areas of developing countries, the access to fresh water is limited even today. Aqueducts are the major structures in water supply and diversion schemes when carrying the water over natural and artificial obstacles such as valleys, rivers, roads, railway lines, canals etc. During an earthquake, the effect of water sloshing on the walls of aqueduct and the resulting hydrodynamic forces is often neglected. In this study, the analysis is carried out for a single span elevated aqueduct using finite element analysis, in which the structure is discretized into smaller elements. The structure is modelled using solid elements in Staad Pro V8i software for different loads. The behavioral response of aqueduct structure subjected to hydrostatic loads and dynamic loads due to seismic ground excitation has been analyzed. It has been observed that the structure is more vulnerable to dynamic loads compared to hydrostatic loads. The effect of dynamic loads due to sloshing of water under seismic forces is predominant. The stresses induced by hydrodynamic loads are observed to be 2.4 times more than hydrostatic loads.

Experimental characterisation and numerical modelling of the resilient behaviour of unbound granular materials for roads

2020-10-19T21:53:31+00:00

This research paper deals with experimental characterisation and numerical modelling of the resilient behaviour of Unbound Granular Materials (UGMs) usually used in road construction. The first part of this paper describes the main results of an experimental program that was carried out to assess the mechanical properties of two local Unbound Granular Materials (UGMs) for construction purposes in road pavement. The second part of this paper is devoted to the numerical modelling of the resilient behaviour of UGMs used in flexible pavements. For this purpose, several nonlinear unbound aggregates constitutive models are implemented within an axi-symmetric finite element code developed to simulate the nonlinear behaviour of pavement structures. In addition, deflection data collected by Falling Weight Deflectometer (FWD) are incorporated into the analysis in order to assess the sensitivity of critical pavement design criteria and pavement design life to the constitutive models. Finally, conclusions of engineering significance are formulated.

Influence of segregation on the performance of self-compacting concrete in the fresh and hardened states

2020-10-19T21:56:00+00:00

The granular mixture represents one of most important parameters in the formulation of self-compacting concretes in order to achieve a representative granular distribution. A good resistance to segregation results in a regular distribution of the different sizes of the aggregates in all parts of the element, with the same granule density. The granular mixture must be homogeneous and representative, and has to be able to flow in the absence of dynamic and static segregation.
The main objective of the present research is to study the influence of segregation on the performance of Self-compacting concrete in the fresh and hardened state, by determining the static segregation index according to the percentage of aggregates of class G 8/15 and that of aggregates of class G 3/8 in order to obtain a homogeneous granular mixture, whatever the volume of self-compacting concrete to be prepared. It is well acknowledged that the threshold of the discontinuation of granular mixing represents a new element with respect to segregation in concrete. The obtained results showed that the percentage of large aggregates has a significant influence on the segregation index and the performance of self-compacting concrete (SCC) at 28 days.

ANN modelling approach for predicting SCC properties - Research considering Algerian experience. Part I. Development and analysis of models

2020-10-19T21:56:58+00:00

This paper presents research on the use of artificial neural networks (ANNs) to predict fresh and hardened properties of self compacting concrete (SCC) made with Algerian materials. A multi-layer perceptron network with 5 nodes, 12 inputs, and 5 outputs is trained and optimized using a database of 167 mixtures collected from literature. The inputs for the ANN models are ordinary Portland cement (Cm), polycarboxylate ether superplasticizer (Sp), river sand (RS), crushed sand (CS), dune sand (DS), Gravel 3/8 (G₁), Gravel 8/15 (G₂), Water (W), Limestone filler (Lim), Marble powder (MP), blast furnace slag (Slag) and natural pozzolan (Pz). Instead, Slump flow (Slump), V-funnel, L-Box, static stability (Pi) and 28 days compressive strength (Rc28) were the outputs of the study. Results indicate that ANN models for data sets collected from literature have a strong potential for predicting 28 days compressive strength. Slump flow, V-funnel time and L-Box ratio could be moderately identified while an acceptable prediction has been obtained for static stability. Results have also confirmed by statistical parameters, Regression plots and residual analysis.

Effect on mechanical properties and stress strain characteristics of normal and high strength concrete at elevated temperature

2020-10-19T21:58:02+00:00

High strength concrete (HSC) has some disadvantages such as brittleness and poor resistance to fire. Fire exposure affects the concrete in way that the disintegration of concrete starts and a severe surface spalling occurs at very high temperatures. Therefore, the structural behaviour or response to the load will change after fire exposure and the structural members may not behave as they were designed. Further, the basics of flexural design depend on the stress- strain response of the concrete which is also affected upon fire exposure. Hence, this study is carried out to provide useful input to aid the provision of a fire resistance for structural behaviour of concrete by investigating the effects on mechanical properties of concrete after exposure to high temperatures up to 600°C and establishing a stress-strain relationship. The concrete cylinders of size 100 mm x 200 mm were exposed to the temperature of 200⁰C, 400⁰C and 600⁰C after which the residual compressive strength, split tensile strength and flexural strength were recorded. For stress strain characteristics, 100 × 200 mm cylinders with polypropylene fiber content of 0.5% by volume of concrete were subjected to temperature exposure of 600⁰C for durations of 1 hour. Curves for reduction factors of strength and stress strain characteristics after fire/elevated temperature exposure has been established. Just consideration of reduced strength for assessment after fire exposure will not serve the purpose as the change in load response and increased deformation capacity also needs to be addressed properly.