The new Concrete.java

package com.tobbestark.MyMod.blocks;

import net.minecraft.block.Block;
import net.minecraft.block.material.Material;
import net.minecraftforge.fml.relauncher.Side;
import net.minecraftforge.fml.relauncher.SideOnly;
import com.tobbestark.MyMod.init.MyModBlocks;

public class Concrete extends Block{

    private Object blockIcon;

    public Concrete(Material materialIn) {
        super(materialIn);
    }

    @Override
    @SideOnly(Side.CLIENT)
    public void registerBlockIcons(IIconRegister icon)
    {
    this.blockIcon = icon.registerIcon("mm:blocks/concrete");
    }

    @Override
    @SideOnly(Side.CLIENT)
    public IIcon getIcon(int face, int metadata){
    Icon blockIcon = concrete;
    return blockIcon;
    }
}