function show_asphalt() {
	div = document.getElementById('asphalt_nav');
	if (div.style.display != 'block') {
		
	close_nav();
	div.style.display = 'block'; 
	
	} else div.style.display = 'none';
}

function show_concrete() {
	div = document.getElementById('concrete_nav');
	if (div.style.display != 'block') {
		
	close_nav();
	div.style.display = 'block'; 
	
	} else div.style.display = 'none';
}

function show_pro() {
	div = document.getElementById('pro_nav');
	if (div.style.display != 'block') {
		
	close_nav();
	div.style.display = 'block'; 
	
	} else div.style.display = 'none';
}

function close_nav() {
		
	div2 = document.getElementById('asphalt_nav' );
		div2.style.display = 'none';	
	div2 = document.getElementById('concrete_nav' );
		div2.style.display = 'none';		
	div2 = document.getElementById('pro_nav' );	
		div2.style.display = 'none';		
}