Advanced techniques for hydrodemolition of a bridge deck 
Per la versione in Italiano: https://www.stradeeautostrade.it/ponti-e-viadotti/tecniche-avanzate-per-lidrodemolizione-di-un-impalcato/
The need to carry out the works by hydrodemolition instead of the traditional cold milling method, was required in the project, and the B.G.F. Srl Company, based in Issogne, in the Aosta Valley region, already boasted previous experience in this technique. Following a market research, the solution was identified in the rental of the Aqua Cutter 710 v robot supplied by HPC srl (High Pressure Company srl of San Donato Milanese – https://www.aquajet.it/).
“Strade & Autostrade” asked the owner of Costruzioni Stradali B.G.F. Srl, Gian Luca Berger.
“Strade & Autostrade”: “Can you talk to us about the Road Construction B.G.F. Srl Company and its history? What are your types of jobs in the area?”.
“Gian Luca Berger”: “Stradali B.G.F. Srl was established in 2005, and it is based on the professionality and availability of workers, vehicles and equipment, and followed from the rental of the Company ISAF Srl, specialized in the construction sector for over 20 years, in particular in the implementation of:
- road works such as bridges, viaducts, motorway sections, inter-provincial roads, etc.;
- cold milling and road paving;
- construction of civil, rural and industrial buildings;
- realization of large and small river regimentation;
- construction of railway works;
- construction of aqueducts, irrigation and evacuation works;
- construction of hydroelectric plants;
- construction of ski lifts, snow-making systems, and ski slopes;
- basin dredging, remediation, environmental protection and environmental engineering operations;
- barriers and road protections;
- special structural works.
In recent years, Costruzioni Stradali B.G.F. Srl has expanded its experience on extraordinary maintenance for roads and motorways works for R.A.V.A., ANAS, SAV, SITRASB and RAV. The Company operates mainly in the Aosta Valley, Piedmont, Lombardy and Liguria regions”.
“S&A”: “You are the first in Italy to use the Aquajet 710 v Aqua Cutter demolition robot: would you like to talk to us in detail about this job?”.
“GLB”: “The works concern the extraordinary maintenance and waterproofing to be carried out on the extrados of the deck of the” Plan “viaduct, located along the motorway link road to the Gran San Bernardo tunnel, commissioned by the Company Società Italiana Traforo Gran San Berardo SITRASB SpA.
The section of viaduct involved in maintenance is included between sections n. 341 and n. 368 and it develops for 272 lm. The road deck has a solid concrete slab of 18 cm thickness, with a static configuration like a continuous beam on five supports, and it ends at the terminations with two overhangs at the side curbs.
In detail, the job includes:
- removal of existing flooring for 2,600 sqm;
- hydrodemolition of 3 to 7 cm slab, according to the concrete conditions;
- passivation of extrados steel bars;
- installation of reinforcement armor;
- concrete casting;
- waterproofing with hood;
- bituminous pavement”.
“S&A”: “What were the main problems you faced?”.
“GLB”: The start-up of a construction site during Covid-19, given the required measures and provisions dictated by DPCM (prime minister decree) and regional ordinances, presented considerable difficulties in programming, transport, supplies, transfer of workers and availability of PPE (Personal Protective Equipment).
Our workers immediately paid close attention to the use of their PPE, complying to the requirements of the safety protocols. The planning of the single construction site activities made it necessary to identify new and different settings of the operating phases, the distance between workers, the use of their own equipment, cleaning, sanitation and training.
The other difficulty was the need to carry out the intervention in two phases to achieve the one-way transit in order to free half of the road, first phase direction of the GSB tunnel, second phase towards Aosta, or 50% of the width of the deck, with deviation of transit on the lane parallel to the construction site.
Given the width of 4-5 m of the work areas and the overall length of the intervention equal to 272 m, it was necessary to set up a mobile construction site, with the following equipment: a semi-trailer for container handling a high-pressure unit of 1,000 bar, 200 l/min. of water flow rate, equipped with a diesel engine with a power of 420 kW, a semi-trailer with a 30,000 liter water tank, supplied by an 18,000 l tanker; an Aquajet Aqua Cutter 710 v robot.
After the completion of the hydrodemolition of the lane in the direction of Gran San Bernardo, the schedule includes the completion of the restoration of the concrete and the construction of the bituminous pavement for phase 1, the exchange of lanes for traffic and the beginning of phase 2”.
“S&A”: “From what considerations came your choice to prefer the Aquajet 710 v robot from Aquajet for hydrodemolition instead of the more traditional system of cold milling?”.
“GLB”: “The project required the hydrodemolition technique and the experience gained in 2019 in another “manual with lance” hydrodemolition site, carried out by our staff and relying on third parties for mechanized hydrodemolition, allowed us to gain knowledge on new and advanced hydrodemolition technologies.
After a market research, between the possibility of assigning third parties (subcontractors) and/or renting suitable equipment, similar solutions had been identified with the use of robot systems based on 2,500 bar high pressure pumps: the lack of immediate availabilsoity of the equipment, given the early start of the job, made the choice fall on the HPC High Pressure Company with daily rental contract for the 1,000 bar high pressure pump, the Aquajet Aqua Cutter 710 v robot, accessory equipment’s and the presence of an expert technician for a training day for our workers.
The experience of our operators in operating machines has allowed us to quickly learn the use of the radio control of the robot. The advanced technology of the robot allows to manage the demolition work in a controlled manner and to expose the metal reinforcement: the robot works automatically and allows the operator to change the parameters of the forward speed, transverse movement of the high pressure jet and longitudinal movement.
The transverse width can also be selected via software according to operating needs. From the first day it was possible to program the work areas, manage the thicknesses to be demolished and check the times required for demolition according to the thicknesses indicated by the Site Management”.
“S&A”: “What are your usage impressions regarding the Aqua Cutter 710 v? Are you satisfied with the choice?”.
“GLB”: “The choice of using this equipment for the hydrodemolition of the deck in question was found to be correct: The Aqua Cutter 710 v has operating characteristics suitable for the demolition of concrete structures for thicknesses of 3-7 cm, with good hourly production and good handling.
Given the amount of water per hour, the equipment requires the placement of a storage tank greater than that present on the pumping unit (3,000 l), to ensure greater operating time margins”.
“S&A”: “How do you rate the assistance received during the period of use of the robot?”.
“GLB”: “The equipment supplied was almost new given the few hours of use, it immediately showed reliability. The only small unexpected event occurred during the first days of use of the equipment, when it was necessary to identify the anomaly caused by a temperature sensor, which stopped the robot, not allowing to use: the problem was immediately identified by telephone with the HPC technician and the replacement of the piece has been scheduled, naturally delayed for a few days due to the Covid-19 emergency.
As soon as the spare part was available, it was replaced, and since then the demolition has continued without interruptions”.
Maximum precision and safety
The Aquajet Aqua Cutter 710 v robot is the hydrodemolition robot that represents the market standard in its category.
The Aqua Cutter 710 v is a machine with approximately 2 tons of operating weight, it is radio-controlled, it is equipped with a diesel engine, it has heavy duty finishing to work in the most adverse construction site conditions, subjected to waste water with sand and debris, designed to balance and handle with maximum precision and safety the counter-force of the water jet generated by pumps even over 1,000 HP.
To control the machine and make it work automatically, there is the software developed by Aquajet that allows many changes, even during work, to adapt to the changing conditions of deteriorated cements.
The Aquajet software is managed by the remote control from the operating area of the machine and is very easy to use, to allow new operators to become immediately efficient and productive. In addition, the 710 v is equipped with a sectional tower that allows you to work up to a height of 7 m, always keeping the counter-force of the water jet under control.
With over 20 years of evolution, the current version of the 710 v allows to perform hydrodemolition from a minimum thickness of a few centimeters up to over 50 cm in complete safety for the operators.
The 710 v is used for the refurbishment of reinforced concrete especially in civil structures such as: bridge decks, tunnel claddings, concrete docks of harbors, piles and columns, building slabs and parking lots, bridge fittings and many other structures.
The 710 v robot is very versatile and can be coupled to different types of high pressure pumps, from 1,000 bar up to 2,800 bar with various motorizations and powers.
Technical data
- Contracting Authority: Società Italiana Traforo Gran San Bernardo SITRASB SpA
- Works management: Eng. Sandro Pariset
- Execution Safety Coordinator: Eng. Daniele Franchin
- Building surveyor: Ivo Surroz
- Team leader: Igor Vaccari
- Executors of the works: Costruzioni Stradali B.G.F. Srl
- Amount of the works: 599,266.30 Euro
- Delivery date: April 28, 2020
Per la versione in Italiano: https://www.stradeeautostrade.it/ponti-e-viadotti/tecniche-avanzate-per-lidrodemolizione-di-un-impalcato/