Use of concrete formulations based on dredging sand in the fabrication of tetrapods for protection of harbour dykes

Port structures (quays and dykes) need an enormous consumption of materials, in particular concrete and its components, as well as sand, hence the need to develop alternative solutions using port dredging sand, estimated at thousands of tonnes through its use in the concrete that forms the blocks of the quay walls. After having demonstrated in a previous work the possibility of using the dredged sand from the port of Agadir in concrete formulations, the present work consists in showing the possibility of using the dredged sand from the port of Agadir in concrete formulations that can be used in the construction of concrete tetrapods from a concrete formulation based on dredged sand, more precisely 50% of the sand entering in the formulation is dredged sand extracted from the port of Agadir. The eventual use of dredged sand in the concrete of the tetrapods will lead to enormous gains in the quantities of sand and thus to a lower consumption of construction materials, and will also play a more important role in the preservation of the marine environment by avoiding the trapping of the dredged materials.


INTRODUCTION
Wave protection structures are structures that protect a port or part of a port against the actions of waves (direct attack, crossings, submersion, erosion, etc.). They are man-made structures, except for natural structures which may have the same functions, among these structures are tetrapod dikes, which are structures that provide protection against waves by placing tetrapods in a shell and a core made of riprap. Tetrapods are four-legged structures, used particularly in hydraulic engineering as part of breakwaters to resist waves and swells.
Typically, tetrapods are made of concrete, not reinforced, and have four members with a curved profile designed to minimize the impact of marine flows. The design of the structure allows the blocks to be interlocked, which, when used in masses, allows coastal protection to be reinforced or even to gain surface areas out of the water on the sea.
The use of tetrapods in particular is very widespread, and their fabrication requires large quantities of concrete and subsequently large quantities of sand, which is why it was necessary to look for alternative solutions to substitute sand and why it is proposed subsequently to replace the sand in the concrete formulations with dredging sand extracted from the port of Agadir. By analysing the different constituents of the concrete formulations studied afterwards, as well as the results obtained, we will conclude on the possibility of finding concrete formulations based on dredging sand able to be used in concrete for tetrapods. -Mixing water which is well water.

Aggregates
The values of the intrinsic and production characteristics of the aggregates are given in the table below:

Sands
The characteristics of the sands are given in the following tables

Other tests carried out on the aggregates and sands of the studied formulation
Laboratory tests were also carried out for the GI and GII aggregates, the crushing sand and the dredging sand from the port of Agadir in order to enable us to make a preliminary decision on the effectiveness of the tetrapod concrete formulation studied.
The autoclave test carried out on the mixture made up of 50% crushed sand and 50% dredging sand qualified the mixture as nonreactive (NR).
Organic materials The expansion value obtained on the mixture (50%SC + 50%SD) is lower than the maximum limit value set by the standard NM 10.1.271, version 2008. Therefore, this mixture is nonreactive with respect to the alkali reaction (NR).

Cement
The cement used is CPJ55 Prise Mer with limestone filler manufactured by the CIMAR plant located in Aït Baha-Agadir. The summary of the results of the cement self-checking tests is attached below. The cement used for the study formulas has a resistance at 28 days is 51.7MPa.

Admixture
The admixture used for this concrete is Sika Maroc's Viscocrète Tempo 1000M, which is a new generation superplasticizer with high water reducer properties.
In self-compacting concretes, SIKA VISCOCRETE TEMPO 1000 M improves stability, limits concrete segregation and makes the formulas less susceptible to variations in water and constituents. SIKA VISCOCRETE TEMPO 1000 M allows a significant reduction of the W/C ratio which improves the durability of the hardened concrete (reduced permeability, increased mechanical resistance, reduced shrinkage).
SIKA VISCOCRETE® TEMPO 1000 M does not contain chlorides or other substances that may cause or promote chloride reactions. The table below lists the characteristics taken from the technical data sheet:

Compatibility tests Admixture and Concrete Constituents
Concrete formulations were studied by analyzing the change and variation in the percentage of admixture in the concrete formulation.
The table below summarizes the results found: 2.3 Nominal composition of the studied concrete formulations of tetrapods based on dredged sand from the port of Agadir The composition of the studied concrete formulation was carried out by the method of Dreux Goriss, thus three formulations were carried out to find the composition of each constituent of the concrete of the tetrapods based on dredged sand and using a 3rd generation admixture to significantly improve the results found. The results of the hardened concretes of the studied formulations are summarized in the following table: The arithmetic mean fcE of the 9 measurements (3 measurements per formula) of the compressive strength measured at 28 days shall satisfy the following 2 conditions: -fcE > fc28 + (Ce_Cmin) -fcE > fc28 + 3

Conclusion
The studied formulation based on dredged sand from the port of Agadir in percentage with crushed sand and materials from the region gave good results and characteristics in terms of mechanical resistance, the formulation has shown that it can be used in the fabrication of tetrapods and that they can be used as protection against swells in port protection works.
The use of dredging sand in the production of tetrapods will allow to make a gain in terms of the deposit of construction materials and to develop the resource of dredging sand of the port of Agadir generally considered as waste.